“what made it interesting was that it was planned support miltiple UIs”
you may are interested into looking into the various LemmyUIs or Lemmy close alternatives like piefed when you like to test out frontends to see their quirks

had to look it up, seems like it

dont know Yunohost

CasaOS is not an operating system and more like a GUI for Docker with access to the terminal via said GUI (at least thats how i used it)
I personally think thats a very good option if you simply want to use an old PC to host stuff and test around but its limited in its scope so if you want things like RAID you need other or additional solutions

TrueNAS is an operating system Might be overkill for a newbie and i think it was ressource intensive but offers a lot of features in return like RAID

Cant really say more because i did not visit the websites recently

Yesterday i managed to successfully host a simple html safely (its more of a network test)
The path is nginx->openwrt->router to internet Now i only need to:

• backup
• set up domain (managing via cloudflare)
• set up certificates
• properly documentbthe setup + some guides on stuff that i will repeat

and then i can throw everything i want on it :D