In Magento2, I tried to follow this procedure. Just before the paragraph, "Theme Logo" I wanted to try to apply the theme already. It ended up in an error, then I decided to restart from 0. I deleted the folder <your Magento install dir>/app/design/frontend/<Vendor>/, cleared all caches, but in Stores > Configuration > General > Design > Design Theme dropdown, I still see the name of my theme… It is apparently written somewhere else, question is where and how to clean it?
Magento 2 – How to Delete a Theme
magento2theme
Best Answer
Themes are saved in database after first install.
So you have to delete the theme in your database also.
There is a table in database named as theme.You can use the below code to delete your theme.
Use dbname; delete from theme where theme_id=5;