Apparently pasting unformatted text in browsers can be done with Ctrl+Shift+V. Pasting it in Office is Ctrl+Alt+V. Always the odd one out. Taken from here: https://devblogs.microsoft.com/oldnewthing/20220906-00/?p=10...

It doesn't work everywhere though as there are still apps that don't offer a plain text paste, and as you have noted the shortcut can be different in different applications.