As far as I know, this is how it suppose to work. Full screen doesn't mean full page.
Opera used to have it but it was having lots of issues so it was replaced by 'save as PDF' that will gibe you a snapshot of the page.
I had the same gripe about Opera when trying it out. There's two solutions
Enable shortcuts in Advanced settings. The default tab cycle hotkey is 1 (back) and 2 (forward). The flaw in this is that the webpage may also be using number input i.e filling forms, youtube.
You can customise a hotkey! This is what I did and there is a tiny learning curve but it's probably well worth it for a great browser! (I'm still new to it).
You can stop Opera from updating itself by entering this code into the Msc Terminal app:
defaults write com.operasoftware.Opera OPDisableAutoUpdate true
Actually, I found Opera 54 to be the most functional version. I am now using version 60 because versions 57 and 58 crashed if I tried to open Preferences, and they were also slow.
@sgunhouse Thanks, no that doesn't help, and it's always there on new windows, restarting, etc. It's somewhat different as the text selection is in a sort of grey thought bubble, this is just white text with a very heavy shadow, no grey bubble.
No, but I would suspect a corrupt Preferences file, which wouldn't be removed when you remove the app and re-install, unless you use something like AppDelete.
(1) Running it in "Safe" mode … restart and hold down Shift when you hear the chime till it's in the process of booting.
(2) Running it logged-in as another user (either as 'Guest' or create one for testing purposes).
(3) On your user account, with Opera closed, find the Opera preferences in ~/Library/Preferences (hold down Alt and click the "Go" menu to access the library) and move the Opera preferences to the desktop. Open Opera, which will create a new preferences file.
If that cures the problem, you know what's wrong; if it doesn't, come back and let us know.
PS And have you tried updating to MacOs 10.14.4, the currrent version?