This was reported long ago already, quite long ago. See Opera opens pages in new tab with Mobile user agent and New version of Opera for Android with UI overhaul threads, for example. I also don't see what is the point, the benefit of closing “outdated” threads, namely if unresolved.
Can this be fixed after 3 years of being reported?
People like me never use a mobile webpage, or very very rarely. Hope you can understand the involved frustration, and fix this. Let me also say that a fully custom user agent would be a nice addition.
Thanks.

Edited the opening post for it to specifically fit this issue.
@leocg said in Webpage rendering artifacts and a few suggestions:

@Barkuti said

This is the whole address bar dissapearing from view, tabs included. Once I tap over some tab it reappears, as it gets re-rendered I guess.

You can change it in Settings > Appearence > Toolbars

With all due respect leocg, I perfectly know where to change the configuration of the browser address/menu bar. But that's not the point. I am reporting an issue, a bug:
.

.
In the above white rectangle is where the browser address/menu bar should show (size is 1920 × 160 in my device). I say “not rendered” for simplicity's sake, although of course I understand it may be being rendered but then some other stuff overlaps a white rectangle above and etc.
This may be related to the other blue bar rendering artifact. I am just reporting and sharing my point of view.
In my experience this is triggered in BLF.

I was going to edit the opening post and delete the unrelated stuff (suggestions and such), but I see it is not allowed now. Cannot agree.

This is to report a couple rendering artifacts which once in a while pop up while browsing BudgetLightForum:
(Hello? Please respect CR/LF characters, they are there for formatting reasons)
.

Self explanatory.
.

This is the whole address bar dissapearing from view, tabs included. Once I tap over some tab it reappears, as it gets re-rendered I guess.

System information:
Android 8.1.0
Lenovo Zuk Z2 running AospExtended-v5.7-OFFICIAL
Opera 60.3.3004.55692 (problem found in many older versions too)

Now, onto the suggestions:
The bookmark manager lacks search function. A search function is more than important, is key. Please add it as soon as possible. Thanks.
Animations. Animations are great in cartoons, but what's the point in a browser? What's the benefit? As I see it, animations reduce the performance of the browser. They're quite fast, I agree. But essentially they're a drawback, and this is bad. Period.
By the way, I see you have restyled the forum. I was going to @#$% it, namely because of the new way to create threads or write posts in a pop up window. But it seems to work well, even with my strange way of doing things. Still, using the whole screen is more practical, in my honest opinion.

@sgunhouse said in YouTube now opening full version of website in browser, not mobile version of YouTube:

Selecting it again should turn it off.

sgunhouse, truufolinski said he had already tried this in the first post.
truufolinski, install Opera Beta 59.0.2904.53502, it's the one I am using and works fine in this regard.

Wow! It's so @#$% to see how Opera can be having soo much bugshite with the user agent thing and interaction with external applications.
@truufolinski, do yourself a favour and uninstall the YouTube application, it's a useless abomination at the service of brother G00gl€. Get NewPipe (available on F-Droid).
Now that I'm here let me say it's hard to find a more shitty site than this one when on mobile. Oh! Well, maybe the G00gl€ help forums.
I am right now using destop user agent, a reduced dpi setting for an effective display size of ≈8.5" and still this crap looks enormous. Suffice to say I don't like mobile sites, I prefer to see full fledged webpages with their full content.

Reporting for Opera beta 59.0.2904.53502. The problem is not yet fully fixed:

https://www.youtube.com/watch?v=OxqteQnh--c

The YouTube thing was fixed, this is 0K. In AliExpress it also works right or so it seems. The only quirk I noticed is the user agent switch in the three dots menu can be a little bit late to update.
But as you can see in the video, Opera is still incorrectly defaulting to mobile user agent or failing to inherit the user agent of the calling on window.
You may already know (or not), but let me say Chrome reads and uses the user agent which finds in the /data/local/chrome-command-line file (permissions: rw- r-- r--). I am only saying this because you (Opera developers) seem to be having difficulties with something which should be as easy as eating ice cream, which at least tells me the underlying engine was never designed (?) to use multiple user agents.

Cheers for now!

Reporting for Opera 57.1.2830.52480 (because of additional user agent flaw in newer versions; check Opera is wrongly opening pages in new tab with mobile user agent). As far as I know, nothing has changed yet in newer versions, though.

Bookmark manager. List of flaws and/or improvement suggestions, in order of importance:

• It lacks a search function, when Chrome has had it for ages already (and I know Opera uses the same engine). This is self explanatory, and rather inconvenient. Please add a bookmark search function.

• It inserts any new bookmark atop the list in any folder. This is counter-intuitive. People who, like me, take care to sort their bookmark tree, are forced to reorder it more often or start thinking downside-up when doing it. Inserting bookmarks at the bottom of the list is preferred, in my honest opinion.

• When sliding bookmarks to reorder them and the screen limits are reached, the scroll animation starts super SLOW and needs A LOT OF TIME to gain momentum. I see no reason for it to be so bad, its stupid. Please let it accelerate MUCH faster and reach a higher top speed too (top speed is slow too). I will also say that being able to slide-move multiple bookmarks at a time could also be nice (multiple selection of bookmarks is already possible via the top right vertical three dots menu).

• When bookmarks are open from the menu, the omnipresent bookmark window takes up the whole screen instead of being open inside a bookmarks tab. This makes impossible to switch to other tabs while keeping the bookmark tree open.

Regards,
Salvador.

I guess Nawodit is probably pinpointing at one of those useless features of the Chrome browser. Useless, you hear me well. As a long time user of Chrome I always had smooth scrolling disabled, and it worked perfectly.
Not because something is implemented means it is good. Bear this in mind.

Hello? Is anyone home?
Reporting for Opera 57.2.2830.52651. Now there is now @#$%ing way for YouTube to be open in desktop mode AT ALL. Are you hearing?
Not only this, if I try to play a video from youtube mobile it opens the video using an external video player in my device (WTF?).
Fix it instead of adding features, please.

This is just to report that, as of Opera version 57.2.2830.52651, which is based on Chrome 80.0.3987.162, Opera's bookmarks manager sucks a little bit. Let me explain what I find missing in Opera (and is present in Chrome since long ago), in order of importance:

• Order of insertion in the bookmarks list. Opera inserts new bookmarks at the top instead of at the bottom of the list. I care to reorder my bookmarks actively, keeping the most used ones at the top of my list or at the top of my folders. Since Opera inserts bookmarks at the top, it forces me to move any newly created or moved bookmark every time.

• Bookmarks manager could remember the last used folder.

• When moving bookmarks, the scroll speed could improve. It is a bit slow (personally I would prefer it far faster).

• Moving multiple bookmarks at once isn't possible. Also not implemented in Chrome yet, it seems.

I uploaded a self-explanatory small video to Youtube. Sorry if it is in portrait, video capture in landscape doesn't works right in my device.
In it I show you the desktop user agent in my Gmail tab, and then proceed to tap over the YouTube link near the upper left corner. The tab which spawns incorrectly goes to YouTube mobile, where I further use the What's my User Agent site and open the three dots menu to prove the thing in case it wasn't CLEAR enough.
Video link: https://youtu.be/gL5clE2-REI