From @philsward in https://github.com/backdrop/backdrop-issues/issues/4829#issuecomment-781...
Also, both Themes and Modules need a "remove/delete" option to completely delete them from the file system. Once a theme or module is installed through the GUI, there is no way to get rid of it from the GUI.
GitHub Issue #:
5320
Recent comments
As I work through things I flush the caches after every change I make. As far as I can tell I have the custom module in the correct place (/modules/custom/fix_zero_search) and the file...
custom module not showing up in modules list
If you haven't already, flush all the caches. If it is in the modules folder whether directly or in a custom folder it will show up. If not, something else is wrong with your site; check...
custom module not showing up in modules list
Awful idea! That's not how modules get installed! The number in db indicates the installed state and schema version. You're not supposed to fiddle in the database directly. There's an...
custom module not showing up in modules list