Software: First and foremost: must be unix-like, must be able to communicate in both ways with an open-wrt router firmware distro and the devices on the local network (android, windows, linux, ipadOS systems). Must be very secure, like enterprise-grade or almost like that. Must be free and open-source. Must be somewhat fault-tolerant (so no Arch or gentoo or anything like that, i don't feel like recompiling the server's system daily). Must have these in base repos or easily installed in other methods: secure ssh client (like openSSH or such caliber), a software that enables me to securely control and see the gui of the server from android (Rustdesk? or such), (optionally i2p, dnscrypt, vpn clients, not needed if the router has them, just in case of emergency), ip camera management software, high-security intrusion-detection system, https server with css and js support (preferably command-line). Window manager: must support a very easy to use and lightweight tiling window manager (like i3wm) or if not, its installation and configuration needs to be possible and documented.
Hardware: affordable, x86_64 architecture, should be able to handle all of these at the same time, without freezing or overheating (i live in Hungary, so should be able to handle up to 40°C air temperature with stock fans or there should be space for more fans. liquid cooling is no-go).
I have considered these operating systems. Are any of these bad ideas? What you recommend that is not here?
AlmaLinux
Alpine Linux
Ubuntu Server
Rhino Linux (unofficial ubuntu rolling)
Debian Testing
Void Linux
FreeBSD
what about Rhino (it is Ubuntu's unofficial rolling distro)?
I'm confused. Your OP seems to describe wanting something stable and "fault-tolerant," but then you go and ask about an unofficial rolling distro? I think you should figure out what your priorities are first.
i have priorities. And fresh software is higher priority that being ultra stable and fault tolerant. I used Tumbleweed which is a rolling release and it was perfectly stable. I would use SUSE server in no question, if it was free
I didn't mean to imply you didn't have priorities, just that a couple of them seemed to be conflicting. To me, what you described called more for reliability than cutting edge. I understand your concern with getting security updates expediently, but you can get those with less system stability risk using a more standard distro.
I haven't used a SUSE in a very long time, but as I recall Tumbleweed is an official product of theirs. I've not heard of Rhino until now, which gives me pause in considering it - let alone the fact it's not backed by a known significant team. There's nothing wrong with that, but when setting up a server like you're describing I'd rather it not require a significant amount of time at random once I've got it up and running, which is what can happen when relying upon less vetted software.
It's your choice, obviously. Rhino looks like it might make a nice desktop to play with, but I personally would really be hesitant to use it for a server because I just don't have the time to deal with problems at random - I've got enough of those already in my life. Your priorities are obviously different, and there's no denying the fact that even things going awry on your server can be a plus from a learning perspective. I would really be concerned with the project being abandoned since it's just a year old, tho.
Good luck whichever way you choose to go.