I set up Linux desktops for elderly relatives who wanted tech support, to universal satisfaction. They seem to not have many issues, since I get fewer than 5 support calls a year total, and I'm an experienced Linux user so fixing anything that does come up is usually easy (<1 of those is actually OS related, they're mostly questions like "how do I do X in LibreOffice again?" or "I got this scam email...").
It's also nice that the DEs I chose are relatively stable, not forcing them to keep up with changes. Running well on old and cheap hardware is also a plus, I couldn't convince anyone to buy a new or even used iMac (and wouldn't want to do that anyway, macOS is far from bug free...).
That said, none of them have self-destructive tendencies and I don't expect to just give them a device and have them set it up themselves.
I have had a great time using Fedora for family members for years! Fedora on a Lenovo laptop has made my OS-related support calls plummet to zero, basically. I check their laptop once or twice a year (during holidays) to upgrade to the latest release.
I spent a few hours setting up Firefox with an uBlock and set up an email client, and that was it.
There was an awkward period where Wayland made screen sharing difficult, but switching to X made TeamViewer work again. From Fedora 39, I switched to using the built-in remote desktop function (RDP) + an always-on Wireguard connection, which makes screen sharing so smooth when I occasionally need to help with non-OS related challenges. This can also be used for SSH access, or whatever.
I recently went with Fedora Silverblue for another relative, which makes everything stay up to date without them noticing. So far it has worked fine, but installing the printer driver was a bit different than usual – but not a problem.
EDIT: Prior experiences has been primarily with macOS, and it has been a lot of trouble adjusting it to their needs and preferences.
I second the Linux recommendation. KDE has a desktop lockdown mode, and if that is not enough there is also a kiosk mode. It's better than foolproof - it is absolutely designed to enable secure, limited access to specific applications.
Same for my mother using ubuntu. She do not know her password (the login is automatic). In case of problem, I connect using ssh.
Most of admin tasks are apt-get update/upgrade, rmdir --ignore-fail-on-non-empty Bureau/* (because she creates empty directory on desktop).
The command cupsenable DeskJet-3630-series allows to unstuck the printer without mouse access (I was on my phone with connectbot).
I have changed the computer after 10 years. It was transparent for her.
It's also nice that the DEs I chose are relatively stable, not forcing them to keep up with changes. Running well on old and cheap hardware is also a plus, I couldn't convince anyone to buy a new or even used iMac (and wouldn't want to do that anyway, macOS is far from bug free...).
That said, none of them have self-destructive tendencies and I don't expect to just give them a device and have them set it up themselves.