What version of Windows, and what type of network?

There was such a setting in Opera 10 (years ago); I don't think current versions have that setting.

Looks fine - check your zoom level (on the menu).

What desktop are you using? Some of them try to arrange windows so there is as little overlap as possible ...

Besides the other half of my answer? Android itself can be set to ignore notifications from particular programs, if desired.

But in the version on my tablet there are 3 options - Ask, Allowed and Denied. This is Opera for Android (not Beta), version 47.3.2249.130976 (I think, hard to read the gray text.)

New Opera does not have this feature - yet anyway. If you want to post in the Feature requests section asking for them to add this feature, you can certainly do that (though check to see if it is already requested first - if it is then add your support to the existing request).

Since Java doesn't work in web browsers any more (not since everyone dropped support for NPAPI plug-ins), I'm really not sure if it matters for "Opera for computers". I have Java because OpenOffice requires it, but this is one of the browser forums and your post has nothing to do with the browser ...

If you use Developer, Sync was disabled in this week's build. Stable seems to be working fine at the moment.

Any page with an on-hover menu, which does not include for example this page. Give us a URL to test it out on. (Something "safe for work" of course.)

As far as OS - in the case of Linux you should include distro (Ubuntu, Debian, etc.), version and desktop (if the distro has more than one available - examples would be Gnome, Mate, LXDE, etc.) Come to think of it, a number of distros are now switching to Wayland instead of Xwindows, so that might be something to mention as well. (Even with Windows you need to specify version, as there are big differences between Windows 7 and Windows 10, but in Linux it is harder.)

Knowing Google, make sure third-party cookies are enabled.

Google does the same, if you use the VPN. Is it necessary for you to use the VPN to connect to Facebook?