I mean, you could charge like $8 and then give the totally real people that are paying that money a blue checkmark? /s
Seriously though, I like the idea, but the verification has got to be easy to do and consistently successful when you do it.
I run my own matrix server, and the most difficult/annoying part of it is the web of trust and verification of users/sessions/devices. It’s a small private server with just a few people, so I just handle all the verification myself. If my wife had to deal with it it would be a non starter.
If it’s a MacBook that no longer gets updates from Apple then it’s probably from around 2014ish, and is definitely an Intel Mac. This is a great candidate for Linux. If you want an environment that is similar to Mac, go with gnome as the desktop environment. Outside of that, any of the major distributions should be fine. I’ve run KDE Neon, Ubuntu, and am currently running fedora on a 2014 iMac and all of them worked without issue.