Your custom module is now fully registered in Joomla 5/6 and ready to be assigned to a template position via Content -> Site Modules!

If you upload the ZIP file via the Joomla backend (System -> Extensions), Joomla places the files in this folder automatically.

However, if you are building this locally and just pasted the folder into the modules directory, Joomla doesn't know it exists yet because it hasn't been registered in the database. You need to use the "Discover" feature:

Log in to your Joomla administrator dashboard.