I'm a career photographer, have been for close to 40 years. I have shot exclusively with Canon products my entire career. In the past few years I've owned a few Canon mirrorless cameras, and I was very eager to purchase the R6 MK II. However I have to say that this is a $2500 waste of money. There are a few pros, like the drive speed, and low light performance, but the cons outweigh everything else.
1) Not compatible with many third party lenses, including Tamron 28-75 F2.8 lenses. Bummer! I have two of these in my kit that are used for sports photography. Had to sell them both, as they won't function.
2) Camera randomly locks up, always at the most inopportune times. It locked up on 3/7/23 and the oddity of it was that when it failed, it displayed the live image that was present in the viewfinder. Not a captured image/photo, but a live image. The unit was unresponsive, nothing worked on the camera. I had to remove the battery and reinstall in order to get the camera back up and running. It has locked up probably 3-4 times in the last month. I'm running the latest firmware v1.1.1, however the lockups happened with the original firmware was well.
3) Custom settings do not keep on this camera at all. I will setup the shooting parameters (including 1/125 shutter speed) that I use, save them as C1-C3 and later when I go to use the setting the shutter speed always drops to 1/40th of a second. An no, I don't have the auto update enabled under this setting. This one is a head scratcher for sure.
4) Painfully slow startup time. I mean like 4-5 seconds before the camera decides it's ready to shoot. Supposedly this was fixed with the firmware v1.1.1, but I haven't noticed a difference. I read on another thread that if bluetooth was disabled, the camera starts up faster. I have experienced that it sometimes starts up sooner, but not all of the time. It's random. If you swap out a battery, and introduce a new battery, expect a 4-5 second lag time before the camera wakes up. I've never experienced this with any other Canon DSLR or mirrorless camera.
My best advice if you are looking to purchase a mirrorless is to go with the Canon RP. This little gem is solid and always ready to go. At under $1000 , you can buy two nice, dependable cameras that won't let you down.