After wallpaper removal, you still need to deal with residual glue. Ignore this step and painted walls may bubble. Either wash glue off (horrible job) or seal it in. Bc the glue is typically water based, it'd reactivate if you seal it with a water-based product. I like an oil based primer like Alkyd Fresh Start by Benjamin Moore. Then, repair any drywall damage, prime with a latex drywall primer, paint.