I used solely rely on a 4gb rpi4, running dietpi (debian-based) and several docker services. This was back in the good old days when they were available and correctly priced. Once I figured everything out it was very easy to set and forget, with the occasional update here and there and very few breakages (because there's very few things to break).

I would do a couple minutes of maintenance 2-3x a month, usually consisting of running dietpi OS updates, updating docker images, and occasionally rebooting the server. With unattended-upgrades and solid security setup prior to bringing stuff live, it was fairly hands off.

The fact is there is no such thing as a TRUE set and forget server, as in "Well, I've set up your server, I'll check in with you in a year or two." Usually there's something that needs to be touched on a regular basis, but if you set it up well enough the hands-on time should be minimal.

Maybe if he trusts you enough to set everything up he can give you remote access via VPN and SSH so you can do a bit of support here and there.