It’s not open source, but I got a lifetime license for Enpass over a decade ago and it’s done everything I’ve ever needed it for. I think stacksocial occasionally has new lifetime codes for sale. I like the idea of Proton Pass as others have said, but it feels a bit like putting all my eggs in one basket, which is a mistake I already made with Google before (context: I use Proton for email). I think Keepass is the next best option if dedicated to staying FOSS.