Apple have released new 27-inch iMacs & tweaked the 21.5-inch models a little. With the latter, no HDDs are available, only various sizes of SSD or a 1 TB Fusion drive.
The action is with the 27-inch iMac. There are 3 tiers, 3.1 GHz 6-core i5; 3.3 GHz 6-core i5 (or 3.6 GHz 10-core i9) & 3.8 GHz 10-core i7 (or 3.6 GHz 10-core i9). All processors are 10th gen Intel.
Some blurb from the website: Faster processors and graphics, expanded memory and storage, enhanced audio and video capabilities, and an even more stunning Retina 5K display with Nano-Texture Glass (AU$750 option) first seen on the Pro Display XDR. Finally Apple has added the 1080p FaceTime webcam that was previously exclusive to the iMac Pro.
The 1st-tier 27-in is restricted to 256 GB SSD with no upgrade available; 2nd-tier 27s have 512 GB, 1 TB or 2 TB SSDs & the 3rd-tier 27s start with 512 GB & have SSDs of 1 TB, 2 TB, 4 TB or 8 TB. I find in incomprehensible that Apple should ship these things with less than 16 GB of RAM, however by not doing so, it's cheaper for the owner to upgrade the memory using non-Apple branded RAM modules.
The 1st-tier is apparently pretty basic, no upgrades to processor type, drive capacity or graphics card. WYSIWYG, aka What You See Is What You Get. However, testing shows that the 3.1 GHz 6-core i5 processor now sports 12 threads, compared to the 6 threads for the 3.0 GHz 6-core i5 from the 2019 base model. The newer graphics card & new processor combine to give greater performance under Cinebench testing that the previous year's high-end 27-in iMac. It also comfortably out-performs any 16-in MacBook Pro.
More info on the Apple website in your country.
In reality it’s just a significant spec-bump.
The bloggers' rumour mill still suggests a new design for the current 21.5-in 4k range with a reduced-bezel 23 or 24-inch size but using the same chassis. Also a 12-in MacBook, a 2-port MacBook Pro, a Mac Mini are rumoured to be most likely to get the first Apple Silicon processors as super high performance is not the aim of such devices.