The top groupsets in both SRAM and Shimano have been 12 speed for a while. I believe the top Campgnolo one is now 13 speed.
Shimano now have 12 speed in the top 3 (Dura-Ace, Ultegra and 105).
For clarity and to pull some odd bits together, mainly about Campag as that's where there's often a lot of confusion because people and shops don't see it as much as Shimano or SRAM ...
SRAM first offered 12s in 2018 but with a single chanring option.
Campagnolo first introduced double chainrings & 12 sprockets at the rear in 2019.
Super Record EPS - Electronic - went 2 x 12s in 2020.
These 12s groups used the same cassette body as Campagnolo introduced in 1999/2000 for (8), 9 & 10s, which also accommodated the 11s cassettes introduced in 2009.
The most recent group, for Model Year 2024, Super Record WRL - Wireless Electronic, is 2 x 12s and uses cassettes with a 10T smallest sprocket, although 1 older 12s cassette, the 11-29, is also factory-tested as suitable for use with WRL. Other 12s cassettes are undergoing factory testing for suitability at the moment.
For the 10T top sprocket, the new cassette body "N3W" is required.
Shimano were the last to the 12s party, in the last model year with a combination of single and double chainring systems on 12s cassettes, in some off-road groups and all the road groups.
Current ranges - in Campagnolo world, all Campagnolo road groups are now 2x12s except:
Centaur 11, which is 2 x 11
Veloce, which is 2 x 10.
Veloce is in the process of phasing out, complete cranksets are no long made.
Campagnolo Ekar, designed predominantly for gravel / CX, is 1 x 13s.
The Campagnolo N3W cassette body is designed to take certain10s and all 11, 12 and 13s cassettes, with those 10s and 11s, and some 12s cassettes requiring an adapter to fit.
The N3W body is shorter than it's precessor and the cassettes which fit it, do so without using the "lost" length.
The adapter splines into the shorter cassette body, restoring it to the length required for the older model cassettes.
12s cassettes that start on a 10T cog don't need the adapter and cannot be fitted with it in place.
13s cassettes don't require the adapter either - and cannot be fitted with it in place.
There is a retro-fit option allowing the N3W body to be fitted to older Campagnolo wheels but only in cases where they can be fitted with a through-axle. N3W can't be used in QR axles. Hence, no 13s and only 12s cassettes with an 11T or larger smallest sprocket, are compatible with quick release.
Shimano and SRAM have both, as others have said, introduced new bodies for some cassettes, according to the smallest sprocket (and therefore, the perceived use) ... Shimano Microspline is a shortened cassette body designed for smallest sprockets of less than 11T, where SRAM have the XD and XDR cassette bodies for smallest sprockets <11T.
Shimano 2 x 12 road offerings still use the 11s HG body.
There is no retro-compatibility between Microspline and HG that I am aware of, nor between XD/XDR and the older "HG-fitting" SRAM cassettes.
<PHEW>!