Disabling PGP decryption in Thunderbird only requires disabling the Enigmail add-on. Your existing keys will remain available on your machine.
First click on the Thunderbird hamburger menu (the three horizontal lines).
2. Select “Add-Ons” from the right side of the menu that appears.
3. This will open the add-ons tab. Click “Disable” in the “Enigmail” row.
Your Thunderbird instance will now be disconnected from PGP.
Once the Enigmail plugin is disabled, your emails will not be automatically decrypted in Thunderbird.