I’ll start off by saying “why not both”. There is no versus. The Rok is certainly more pervasive across the US. Pick races that make economical sense for you. Also, strongly consider sim racing as a part of your repertoire. Race where your budget is biggest… ie consider 206.
The only thing stopping you from running F4 right now is money. You could (arguably) enter a NASCAR truck race if you have the budget.
Do karting for fun, gain experience, driving one of the most perfect handling vehicles around and make awesome friends. The ladder is paved with money and connections first, everything else is secondary.
Honestly, if I was aiming for a ”pro” gig in racing I’d reduce my focus on karting and keep spending to a minimum on it. Sure you see racers who started there, that doesn’t make it required and there are a lot of other factors that got those drivers to that level. For every one of those drivers there are literally 1000’s that spent too much in karting and ran out of coin before they could do anything in cars.
Focus on networking and relationships. Work with various teams. Build your own audience and help other drivers and brands build theirs.
Use sim racing as a tool to gain racing experience and also ride the exposure train while it’s rolling.