The loop is great!

I found out, that I don't have this problem in Opera on my other computer (identical version and identical configuration and identical system). I reinstalled Opera and everything works fine now.

I don't like the pages preview on Ctrl+Tab.
So I remapped Ctrl+Tab from "cycle" to "switch right through tabs".
Now I cannot cycle from last tab into the first one.
Does anyone have idea how to fix it?

OK, problem is solved for me.

I opened Opera, windows setting panel showed up, like always.
I change default browser to Edge and default mail program to Mail.
Then I closed Opera, opened it again and setting panel did not showed up!
So I closed Opera, opened Windows setting by myself and changed Opera to my default browser.
And everything works.

I'm quite sure I tried this before, so maybe some magic is involved.
I hope I helped somebody.

The only thread I found is this: https://forums.opera.com/topic/16423/opera-on-windows-10-acting-strange
It's closed and it ends with: "Oh, never mind, I will use some other browser... Who cares... Anyway, thank you all for your time!"

I didn't found solution, so if somebody knows something, don't hesitate to help.

I found out, that setting panel is not showing up, if I run Opera as Admin user (with I don't want to do, obviously).

Each time I run Opera I see window with default program configuration: http://screencast.com/t/o85mzHUgwxm. It opens each time and drives me crazy. How to get rid of this?

To start Opera I click on shortcut linked to "C:\Program Files (x86)\Opera\launcher.exe".

Opera is my default browser: http://screencast.com/t/pRnUx0QImJD.
I use Windows 7
I use Opera 39.0.2256.48

After enabling "Proprietary media types" flag I have issues on some sites in Opera 23. For example this site crashes: https://www.kickstarter.com/projects/2091647642/skea-smart-kegel-exercise-aid (don't judge).
It works fine after disabling "Proprietary media types".
I don't recommend to change this flag in Opera 23 to anyone.
It works fine in Opera 24.

One more hint: I found Vimium extention very usefull:
https://chrome.google.com/webstore/detail/vimium/dbepggeogbaibhgnhhndojpepiihcmeb

usage:

1. press f
2. shortcuts to all links will show up

This is Chrome extension, so you need to install this extension first:
https://addons.opera.com/pl/extensions/details/download-chrome-extension-9/

There is no such feature in new Opera, like searching for the link. However, you can still search for a text and you can use this feature in navigation purpose:

1. Ctrl+F
2. search for a text
3. hopefully you are on the link, if not, use F3
4. Ctrl+Enter

I can confirm exactly the same behaviour on Windows 7.
After changing "Proprietary media types" flag, the page crashes in 23, but works in 24.

Thank you for your help.