For private use? Hot take, but Arch. It’s easy to maintain and not easy to break at all. I think I spend zero time on maintenance other than running package updates. I only reinstall when I get a new computer.
(I say for private use only because you’ll be getting weird looks from people if you use arch on a server in a professional setting, and it might break if you try to update it after five years of not doing it since there aren’t any “releases” to group big changes - in practice I run arch on my home server too with no issues)
My experience with Matrix is that the federation itself is a deal breaker. I have a pretty beefy server and good connection which was getting ddosed by running Matrix and timing out on so many requests for avatars/profiles etc. Maybe I did something wrong, but the whole experience rendered me quite skeptical to the viability of it as a federated chat.
That said I’ve had nothing but good experiences using it with big servers set up by pros.