I was a bit surprised when I swapped on an IRIX EF lens to the R6m2 that has worked well for the R6 and R5 and found that when taking a photo it simply froze the camera requiring the battery to be removed. I tested it a few times and it repeated the issue. I tried the video mode and to my surprise it worked fine.
I contacted IRIX and apparently it really is a thing they are going to have to work through. I suggest you contact IRIX USA if you are having issues, they may have to reprogram your lens based on their comments to me.
To check on the R6m2 I tried a number of lenses to see if they function. All lenses were also tested with the R6 and R5 (firmware 1.8.1) and all functioned correctly.
Lenses that did not function in photo mode but did function in video mode on the R6m2
Photography versions of the IRIX 15, IRIX 21, IRIX 45
The IRIX 150 mm CINE Macro lens functioned correctly in both photo and video mode.
Also the following Sigma lenses all worked fine with the R6m2 the 35mm, 24-70mm, 70-200mm, 135 mm, and the 150-600mm Sport.
Update: I am happy to report that Sarah and IRIX provided great service and that now all of my IRIX photography lenses for the Canon work great with my Canon R6m2! Thanks Sarah and IRIX! I had to send them back to IRIX in Colorado and they performed an update to the lenses. I imagine that moving forward the lenses will have the necessary firmware but you may buy a new one that was from a lot that had not been updated (like I did recently) – just contact IRIX so they can make it right.
Recently acquired 30mm from B&H that also did not function properly with the R6m2; Thanks to IRIX for making it right (and quickly too!).