For those that don't want to go back to the Dark side (Reddit), the post referenced a theme (Grey Layout global theme) which got KDE Dev's involved who in reaction removed the listing from the store.
In short - the theme ran code to run a rm -rf on the user's drive which wiped everything during install. Aside from backing up your data religiously, be sure to inspect the code instead of blindly installing for now. KDE Dev's said they will need to do better so I expect some changes are afoot to provide better security.
Themes are very powerful beings in KDE. they can install SDDM themes and scripts, they can set Kvantum themes, custom parameters for other parts of the system etc.
It’s really not uncommon for a lot of themes to package an installer script, in case they have multiple versions, or multiple colors bundled. Realistically, they should just each have their own store page, but it’s a colossal pain in the ass. The Catppuccin global theme, for example, has 16 color variants, 2 decoration variants each, and then also a version with no splash. The whitesur theme is similar.
I do agree though that if this is going to continue to exist, it should not have permissions it has today
Stupid question maybe, but would your backups even be safe? Sure, it was mentioned that you had to enter your sudo password, but let's say you did that because you are careless, "rm -rf" would wipe all connected and mounted drives as well, so your backups would be gone, wouldn't they? Or does Timeshift mount and unmount on demand? If so, what would happen if you ran "rm -rf" while a backup is being saved?! It seems to me that a simple "make backups" isn't enough here.
I do not know much about Timeshift and Lucky backup. But a proper backup is not a on the same system even if it is a second drive internally. For some quick file recovery after deleting things you shouldn't have it is fine. A proper backup should be a separate system and ideally 2 systems one externally but this is overkill for most folks. With a separate system you can setup automated backups and disaster recovery. if you are scared the backup system can get compromised from the main system. you can set things up in such a way that the backup works in pull mode and the main system being backed up has no access to the backup system.
This is different from the Wayland security model, as Wayland restricts the ability for clients to modify and read from other clients arbitrarily. This is an extension to a Wayland compositor, and as all extensions do, it contains code which runs on your system. Any code, unless sandboxed, can access your filesystem no matter if it's run under Wayland, X11, or no windowing system at all for that matter.