I Downloaded it myself and have about 5-10fps in the main menu on a RTX3090 64GB , 3950X. Most of the reviews say the same. Colossal Order are suggesting you should play on very low detail. I was a massive fan of the original having played Sim City since 1993 but I cant even get into this. It shouldnt have been released so early IMO
Game's still selling on Steam. And to my knowledge, Workshop integration is a "free" service to both the publisher and player (supported by the 30% sale cut).