Text is copied to your instance's database, but any images are hosted on the other instances and simply linked to. Worst case scenario, you get told to delete something that's illegal in the country in which you host the instance, you comply, and everything's peachy.
Edit: That being said, I'm currently hosting an instance for myself and a few friends, and it's been smooth-sailing. Just make sure to require email verification or admin approval for new sign-ups (or disable them entirely) if you don't want to be overrun with bots.
If you're strongly tied to KDE and immutability, then I would say no. There's not really an equivalent distro that provides stable immutability with a solid KDE/Plasma experience.
If you're tied to immutability, but not KDE, then I recommend openSUSE Aeon. It's Gnome, but with a few extensions, feels great as a KDE replacement. openSUSE Kalpa (KDE) exists, but is in a very rough alpha state and was mostly unusable for my purposes.
If you're tied to KDE and not immutability, then I recommend really any other distro. Can't go wrong with Arch, Nix, or even Debian if you don't mind slightly outdated packages (and that might be false now, I believe it just had a big release?).
Jerboa is the official Lemmy app created by the Lemmy developers. It's unfortunately not a super great experience at the moment, but it's improving quickly with all the attention on the fediverse. I use the mobile site as a PWA, but I keep Jerboa installed and try it every now and then. I'll make the switch permanent soon, I'm sure, given the rapid development.
Edit: Forgot to mention it's available both on F-Droid and Google Play, in case you avoid Google services on your device.
Text is copied to your instance's database, but any images are hosted on the other instances and simply linked to. Worst case scenario, you get told to delete something that's illegal in the country in which you host the instance, you comply, and everything's peachy.
Edit: That being said, I'm currently hosting an instance for myself and a few friends, and it's been smooth-sailing. Just make sure to require email verification or admin approval for new sign-ups (or disable them entirely) if you don't want to be overrun with bots.