@_elena
> I'm in Ubuntu (the latest version)
I've mostly used Ubuntu derivatives. Especially Trisquel, which I recommend to anyone whose graphics and WiFi chips can run without proprietary blobs. Also spent time on Mint and LMDE.
> I was trying to copy text from Vivaldi and paste it into Terminal. I was pressing Shift + Ctrl + c and Shift + Ctrl + v
What I would expect to work is CTRL+c in Vivaldi, and CTRL+SHIFT+V in Terminal. Caps lock should reverse everything, not fix it. Maybe a bug?