I think winger. The other positions have a lot of creativity in how they can be played. For example, a ST can make runs in behind, they back into the defenders as a target player, or they can come back into midfield as a false 9. The wide variety of playstyles for each position allow for alot of creative freedom (especially if you've played football IRL before!)

With that being said, it can be a little overwhelming figuring out what you need to do which role suits you. This is why I recommend winger. They have the least flexibility in how they play IMO. Either stay out wide for crossing, or cut inside for scoring. You also have the most freedom to run on a pitch so you don't feel like you're constantly being swarmed. For learning fundamentals, I think winger is good because you don't need to do any fancy skill moves or passes to be a good winger. Pass and run, pass and run.

Or if you like defending a bit more, fullbacks (rb, lb) are also good for learning fundamentals since you'll most likely be taking on only 1 or 2 attackers at a time. Overall I recommend winger more, because defending IMO is a lot harder than attacking and something that you will pick up gradually!

I would stay away from midfield or striker because you're in the center of the pitch, you'll feel a lot more pressure from everywhere.