the hidden "trashbin", .Trash-$(uid), invented by Ubuntu

This isn't some “idiotic principle invented by Ubuntu”, it just follows the freedesktop.org Trash specification. For many users, it can be really beneficial, see also the spec's introduction:

An ability to recover accidentally deleted files has become the de facto standard for today's desktop user experience.

Users do not expect that anything they delete is permanently gone. Instead, they are used to a “Trash can” metaphor. A deleted document ends up in a “Trash can”, and stays there at least for some time — until the can is manually or automatically cleaned.

Whether an application like Prism Launcher should use the trash can or delete the files directly is an entirely different question.

I use command trash-empty to empty all trashcan of all the users, after each system update. It's a non standard program, but most likely available in your distributions repository: github.com/andreafrancia/trash… And my alias/function will show each file that is about being deleted (just put it in .bashrc, if you have installed trash-cli, which includes trash-empty):

::: spoiler old function (click to expand)

empty() {
    echo "Files to delete:"
    trash-empty -f --dry-run |
        awk '{print $3}' |
        grep -vF '/info/'
    echo
    trash-empty
}

Edit: After I posted I just realized there is a more straightforward way of doing it:

New and more simple alias:

alias empty='trash-empty -f --dry-run ; trash-empty'

I'm more of a dust man, myself. It runs recursively so it's easy to pinpoint the culprit.

[Image source: the project's README]