Depends on the panel. if it is solid wood, I assume it will move with humidity and finish it and the inner edge of the rails and stiles prior to assembly. If it is plywood I finish after assembly and usually put a little glue in the panel groove to strengthen the door.
The last batch I did that way, same.Exactly the same.
Sky, welcome to come over anytime. I try and do 25 hours a week in the shop, but right now on overload.Willhem, wipe your panels with a wet rag before finish sanding, this raises grain, first with the wet, let them sit for a few minutes, wipe with a dry cloth, let them dry, then sand. I always put at least one coat of paint on before assembly.
ttps://www.rustoleum.com/product-catalog/consumer-brands/zinsser/primer-sealers/cover-stain-oil-base-prime, they make this in water base, fantabulous, 30 min dry lets you get almost glass finishes, 30 min dry