You’re updating an older home and thus have permanently removed an interior door from its jamb. Now the recesses for the door hinge and strike plate remain. You could just paint over them, but it’ll look a whole lot more attractive if they’re gone.
This means filling the door hinge with putty, and sanding. It can take several applications and lots of time. And the results might still be less than ideal.
The answer? First fill the recess with a piece of a paint stir stick. You’ll find the thickness of the stick is close to the depth of the recess. Cut to size, glue in place, use one coat of putty to fill in around the patch. A quick sanding, a touch of matching paint and it should look as good as new.