You added a Custom Post Type through the plugin ‘PODS’, but instead of the Gutenberg Editor you see the Classic Editor, when you edit the Custom Post Type.
This is what you do:
Edit the POD, (in my case called ‘Memories’), click on the Rest API tab, click on ‘Enable’, and then select ‘Show All Fields’ and ‘Allow All Fields To Be Updated’
Do the same for any other type of Custom Post Type you make through PODS, such as a Custom Category or a Custom Taxonomy.