→ → Applications Menu Extension
You want to use the GNOME Applications menu but see in Tweaks that the extension hasn't loaded and can't be enabled?
From Show Applications open the Utilities folder and open Tilix
Copy and paste the follow into Tilix as shown below...
sudo apt install gnome-menus
and hit enter. You'll need to type in your password and follow the prompts.
Once it has completed then log out and log back into PureOS.
Once your computer has booted, go into Tweaks and you should be able to enable the Applications menu extension for GNOME.