Same thing happened to me - told my boss on a Friday that I had received a job offer with a 55% pay raise and was probably going to take it, so we should think about off-boarding. Later that day my admin rights to the gitlab org were removed, was told that "it was a mistake", and was fired the following Monday.

They also took my $20k bonus that I was supposed to receive months earlier and used it as a carrot on a stick to get me to sign a bunch of legal paperwork releasing all my rights. At least I got the much needed money. I was really underpaid there.

I also lost my best friend who also worked there that decided to side with my boss and the company. lol It was a bad time.