Re: Cannot click accept or decline on the invite from last squad pop-up

That tends to work with Origin usually, at least on my setups. Can you try restarting with a Clean Boot (and you can keep the Nvidia overlay and Origin in-game active) and try accepting the invite again after your next match?

https://help.ea.com/en-us/help/faq/how-to-clean-boot-your-pc/