Got it thanks, I think it’s weird it shows up in Dolphin this way but at least I know what it is now.

Calibre installs fine (flatpak). I updated my post but I was able to change the temp directory which “fixed” it.

Appreciate the response, I updated my post but I “fixed” this by changing Calibre’s temp directory.

You were correct, I believe I “fixed” the error with Calibre by using Flatseal to add an environment variable CALIBRE_TEMP_DIR that changed the Temp directory to something else.

It’s not in partition manager actually!

Not clear, the “drive” doesn’t show up in partition manager.

That makes sense, thank you! How can I clear up space in it?

How’d it get full then? And if it’s supposed to be 100%, any ideas on how can I get Calibre (so far the only app I’ve noticed that is giving trouble) to ignore it?

I commented elsewhere, but I do a lot of customizing and immutability has not proven to be even the slightest barrier for me in over six months now.

fwiw I am a power user by Windows standards (n00b by Linux standards) which is to say I tweak a lot of settings and do a lot of customization, and in six months of using Kinoite I have not encountered a single thing I wanted to do but couldn’t because of it’s immutability.

This is an excellent answer. Kinoite (basically the same thing as Aurora) is what enabled me to finally make the switch to full time linux a few months ago.