It would depend on the kind of feature layer. Is it a hosted layer (all the data was copied when published) or published through a registered server?
If it's hosted, check the settings on the layer to make sure that editing is enabled.
Also, if the layer was added to Pro before settings were changed in AGOL, sometimes you need to re-add the layer to your Pro project for it to pick up settings changes.
- Josh Carlson
Kendall County GIS