Bitwarden is free, open source, and has support for all platforms. There are more secure solutions if you're really paranoid about it but this is great for most cases
100% backing this, especially since they recently moved away from that awful .NET MAUI app and made native apps for both iOS and Android.
I don't use it personally because I still just manage my passwords offline with Keepassxc on my computer, but I recommend BitWarden. Especially over Lastpass.
it's a file format. Any application that says it can use keepass databases should work. Thrre are lots of iOS apps that are comptible and KeePassXC on Windows (or Linux) is the best desktop application. You usually just have your database as a local file but applications also usually support remote databases on a file server, at least on iOS. KeePassXC doesn't have much remote file support built in.
If you are a normal human being then bitwarden is currently the best option. If you are into computer shit you can use keepass, which has clients on all platforms but you will have to figure out how to sync your keepass database across devices. Or if you are like me who uses esoteric solutions because it is a thin thread by which my individuality hangs then you can use passwordstore.org, which has worked fine with me on windows, linux and android.