its an open standard to do these kbdx files that in the lastest iteration can be encrypted with a passphrase, a file or even with yubikey or hardware like that (I'm not much familiar with that, but there are a lot of client supporting it).

It all started with a desktop client, the original keepass for desktop in, I think, early 2000s and now there are multiple client cross platform to handle the database (the best and most compatible today are keepassXC on desktop and keepassDX for android, I'm not familiar with ios world but I'm pretty sure there is at least a good client to use).

The "cross platform functionality" could be achieved moving your encrypted passexample.kbdx file across yoir devices, a great combo is use something like synctin to sync realtime the update to the file, so to have your update passwords to all your devices.

Its easy UX to start with a single device, a bit techie to do your great multi-devices set-up