Not sure this is what you are looking for, but syncthing is for self-hosting and it’s Peer-2-Peer. I use it to synchronize my important documents and photos across my devices, it has options for encryption and file versioning.
Syncthing is the 3 in my 3-2-1 backup strategy. It enables me to maintain 3 copies of my files: desktop, phone, NAS
openmediavault and casas are good noob-friendly OSes for NAS purpose. Much faster and simpler to get it running than some Proxmox and True NAS overkill solution.
You can also just install whatever Linux OS you like, and plug-in some screen, keyboard and mouse and do your setup this way, like any other computer!
For Hardware, I recommend to build a computer out of standard parts. For what you said, a small motherboard with an integrated Intel N100 CPU and a nice looking case like the Jonsbo N2 will sever you well. This is very close to my current setup, using an older j5040 CPU and it runs everything just fine with no effort (Jellyfin w/ light transcoding, *arr stack, Usenet and torrent clients, syncthing, SMB and NFS filesharing, and more)
I second this proposition of DIY build. My current build is an older version of this using an ASRock motherboard with integrated Intel j5040. It’s already very capable! I run Jellyfin with HW transcoding and a dozen other containers and there is still plenty of headroom.
The Jonsbo N2 case is pricey but good quality, nice looking and nice to build with ! Cheaper options are there but not as nice in terms of looks and usability.
IDK, I have the same experience. It takes 10 good seconds to open the file manager on my win11 work PC with 32GB of ram and 12x CPU threads. It also takes 5 minutes from power up to usable desktop. My Clevo laptop from 2011 with 4x cores and 8GB of RAM sporting Debian is much smoother to operate.