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
The preview builds for reviewers and streamers had serious performance issues, then they warned the public about serious performance issues, and then the release version has serious performance issues. Yes, sounds like they just forgot to press some switch and the fix that once and forever solves all performance issues is scheduled to arrive today.