I just found the solutions. Looks like the Portfolio project does not play nice with Gutenberg. I’ve changed it to another editor (WP Bakery I think) and then you can enable the field on the field options.
I’ve been working with this theme for years, never had much problems, but sometimes it is a bit hard to find where the feature has gone…
Got the same problem. Any solutions yet?
There is no project cover property in the right sidebar. Is there a workaround so I can do this directly in SQL or something?