If you want a larger or more powerful desktop Mac than the 24-inch iMac, then you are going to have to settle for the Mac Studio and Studio Display, Apple's latest products. For some reason, Apple has decided to stop selling the 27-inch iMac before offering a successor, which is now rumoured to arrive sometime next year.
https://www.notebookcheck.net/Apple-ends-the-27-inch-iMac-without-offering-a-direct-replacement.607310.0.html