'We’re saying goodbye to the Bethesda.net Launcher this year. Starting in early April you’ll be able to migrate your games and Wallet to your Steam account. For more details on what this process will look like, read on.'
more details on how to migrate in early april. but for now...
main FAQ
https://bethesda.net/en/article/2RXx...ating-to-steam
Fallout 76 FAQ
https://fallout.bethesda.net/en/arti...fallout-76-faq
edit
note . this main OP has been updated to include the new links from AGTDenton (saves me doing it, because i forgot )