No idea what is involved in adding a new plug-in to the sidebar, but if you are going to have Telegram & VK, might as well add Threads. Figured it might be simpler now they have a web-based version.

You are right in every respect.
And no amount of uninstalling and re-installing of browser, plug-in etc will make a difference.
In brief, Opera are a bunch of arse.
I will be using a different browser until an update fixes what is a cruel and unusual cockup.
Courage.