I can relate because my dad is 84 and he really struggles with simple things like entering a password to sign in to Gmail. He forgets what he did last time and so I'm back to explaining how moving his mouse causes the pointy-arrow thing move around on the screen, to get it pointed at the wide rectangle near the middle of the screen, etc. No UI library is going to solve his struggles.

I solved most of the sign-in problem for my dad by picking a simpler browser than Google Chrome, and by tweaking his browser settings to be just-so. That's not going to be much help for you, the website creator...

Maybe allow passkeys for login? These days, passkeys usually get stored/supplied by the underlying OS. (By usually, I mean that's the statistically most common source of the passkey today. They can also come from a browser plugin or a hardware key.)