The way this was done, and is still listed in the manual, is by adding luts to the folder System>Library>Application Support>Adobe>Common>LUTS> "Technical" folder or "Creative" folder.
on my system those folders no longer exist. I recenty upgraded to Premiere 2022. Instead there are "Input" and "Output" Luts folders. I tried putting my luts in here, but alas, they do not appear in the Lumetri dropdowns.
Where the heck are we supposed to put our LUTS? Even the Adobe documentation seems to have it wrong.... but i'm hoping it's me!
Totally understand that Adobe, as a mom and pop company with only a handful of clients, looks past such details in their official documentation. Makes it really fun for people who rely on their software for their livelihood.