The "Calculate coordinates using address" feature of Page Forms is blocked by the CSP directive, which currently only allows tile.openstreetmap.org and *.tile.openstreetmap.org. The coordinates lookup goes to https://nominatim.openstreetmap.org. If possible I think it's safe to allow all of openstreetmap.org.
For example, go to https://spcodex.wiki/wiki/Special:FormEdit/New_venue/Foo and put in an address in the field before the "Calculate coordinates using address" button, then click the button.