Recommend sealant for a front door (exterior)

If is the exterior door you should use whetershield paint is better then the normal oil base paint im afraid you have to sand the door aplly the primer or undercoat whetershield and after use the paint

It will make a difference what the door is made of. If it's a PVC composite or alluminium door you really need a dedicated primer. Once it's primed you can use most exterior wood paint products but some are better than others. AS you have already done the painting you might just have to wait and see how it performs and if it starts to fail, sand it all back and start over.

I think that the best paint as a finish and durability for many years should be used whetershield paint that is better than normal oil-based paint.

All depends on what the door is made of? When you say you’ve just realised it’s wood paint and not the correct one what’s the door material ? Wood or pvc. Thanks

I would recommend to give it a good sand down apply a coat of weathershield primer undercoat plus two coats of weathershield gloss so properly seal it. It will last longer than usual oil based paint.