Huh? I’ve seen zero implementations that work seamlessly across computer, phone, tablet - unless they are all single platform, which I have yet to see anyone actually pull off.
There are nearly countless ones - 1password for example works everywhere, as does Roboform, bitwarden, keepass, LastPass, nordpass, and many others.
All sync seamlessly and support the major (and often minor) browsers.
Google Password Manager, Bitwarden, 1Password among many others.
It's a beautifully simple experience for Apple users across all their devices.
I can't speak for other platforms; I stopped helping ${EXTENDED_FAMILY} with non-Apple questions because the crap I had to diagnose, debug and deal with for Windows and Android was worse than ${DAY_JOB}.