I wasn't sure if this is an actual bug or an something that was intended by design. Reading the Issue Reporting page in the KDE Community Wiki gives me the impression that it might fall under the "Vague and subjective matters of aesthetics or personal preference". I thought it might, at the very least, be worth a discussion here on the forum. The topic relates to brush preset naming.

If I delete a brush preset I've made previously via the "Choose brush preset" icon, and then try to save a new brush preset, Krita says that the filename is already in use by another resource, despite the previous brush preset already being deleted. It gives me the option to try and overwrite the resource but continuing with this option will result in failure to overwrite the resource (presumably, it is been marked as deleted).

Reloading the program and then trying to save the preset with that same name doesn't work either. Going into the Settings/Manage Resources window and then checking "Show deleted resources" checkbox shows the previous brush preset with the name that I want to use. Presumably this done to allow people to restore brushes that were deleted by accident. However, if I actually want to be able to use the name, I would need to go into the resource folder (in my case, ~/.local/share/krita/painttoppresets/) and then delete the brush preset that's using the name I want to use.

I personally think that this is an unnecessary extra step but I'm not sure if this is an intentional design. If so then maybe we could have a button to permanently delete a brush in the Manage Resources window while the checkbox for showing deleted presets is enabled; just underneath the "Undelete Resources" button perhaps?.

I would've expected that if a brush is deleted, that it is gone and then the name should be free to reuse. However, I can also see why being able to restore brushes that were accidentally deleted would be useful. If the above suggestion isn't ideal, then maybe append the deleted brush's .kpp file name with "_deleted" or something similar, although there may be a problem should a user; delete a brush, reuse the name for a new brush preset, suddenly decide to restore the previously deleted brush but then can't use the name because it's being used. In this case, you probably need to put in checks for that and generally more work.

In terms of my setup, I'm using an AppImage of Krita version 5.0.0, although I've tested this on version 5.0.2 and it's still the same. I'm on Kubuntu 20.04.4 LTS.