Fun fact: They also ship curl.exe, which is different from curl in PowerShell, as the latter is an alias to Invoke-WebRequest. That's one of the insanest decisions they could make during one of the sanest ones.
Most of the companies behind it (including NextCloud itself & IONOS) are providing a document cloud to their users already & are used to maintaining Open Source, so I would indeed assume some seriousness here.
That sounds like you might like VyOS. I found it to be relatively easy to achieve exactly what I wanted, but went back to a GUI as it turned out I wanted a pet and not start a farm.
The DC side is fully isolated except through a capacitor that is there to reduce EMI interference and is specifically built to "fail safe", except for the cheapest no-name imported power supplies. (https://www.pcbaaa.com/y1-capacitors-function-application-an...)
The main problem is the bugginess in combination with the featurelessness. Usually you can work around bugs in some way or another, but many of the bugs in Boxes seem to come from the fact that control is taken away from the user in the first place, and there's no way around it except touching the source code.