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PSA: Remember to also check hidden directories you don't even know about for waste of space
(feddit.org)
Apparently, Prism Launcher chose to adhere to the idiotic principle of the hidden "trashbin", .Trash-$(uid), invented by Ubuntu. Even though it's based on QT. This can't be disabled. It accumulated 139 GB of literal Trash, fully replaceable, over time. Just ... why? There's even an open issue about this, for over a year, referenced multiple times. I guess I have another point on my agenda.
Your desktop environment should have settings for when to clear the trash. You can also use autotrash to clear it automatically.
The Problem is: I don't have a DE, and therefore didn't realize programs would still try to use trashbins.
Wait... How do you not have a DE but are using something like Prism Launcher? :/
With a plain WM, sway to be exact.
A window manager is only there to - well - manage the windows of programs. A DE provides a WM (eg. KDE has Kwin) as well as tools (eg. Discover, a detault file manager, settings programs) and a few other minor things. They also usually have less configurable WMs, usually stacking (with freeform windows that can hover above each other). As I don't need any of that, just a way to move windows between screens and workspaces, a plain tiling WM is perfectly fine, and more flexible.
The only thing I need a file manager for is to get a quick overview over many images, and for that I use lf, in a terminal.