Usually some of us 18-21 are trying to swap to the 2022 style, not the other way around. I'm in the process of doing a 2022 taillight bar and I want to go with the kdm spec sequential turn signals. In order to get the 2022 light bar on my 2020 (which i haven't quite figured out fully) holes in the trunk lid have to be drilled out to get the new light to fit.
I did this, light still doesn't fit. Each side has red tabs that I had to shave down as well, fits better, still not quite snug like the stock unit. The positions of the red tabs are different on the 18-21 models. Now I have to try to shave down the 2 black pegs and 1 red peg on the center part, hopefully that works.
One thing I noticed about the taillights is that the 2018-2021 is concave while the 2022 is convex. So if you don't have the full matching pieces of either, it will look odd. Not sure if you can tell exactly what I mean by the pics or not?