I think this will provide some clarification. Essentially Game play wise there are still 8 Gyms like normal. It's just lore wise there are 18 Gyms but that are supposedly competing to be one of those 8 Gyms, but you won't see the other 10 Gyms in the actual game. It's more just the explanation of why some gyms are in one version and not the other and it builds out the world.
https://www.gameinformer.com/2019/10/03/the-pokemon-company-clarifies-there-are-not-18-gyms-in-sword…