I can confirm that followers are gradually re-added automatically over 24-48 hours. It takes time for the system to catch up with a reinstatement, particularly with that number of followers. Probably takes longer now Musk has fired everyone.And yet I didn't have to refollow him.
I presume, over a period of time, all those who followed him when his account was suspended will automatically find themselves following him again.
Either that, or some complete arse has taken over Twitter and there's no rhyme or reason to what is going on.