The two I can think of offhand:
Trying to get Rocksmith 2014 to work with my Real Tone Cable, which I did have working for a while. Using Pulse Audio, the audio works perfectly except the game doesn't see the cable, I suspect because Pulse is processing it like a microphone. The fix is to set Proton to use Alsa for audio and set Pulse to disable that device so it is available to the game. Now, when I launch it, the audio is horribly corrupted and the input from the cable is all over the place. This isn't caused by Cinnamon because it happens in KDE too.
The part I suspect is a Cinnamon issue is the graphics flash in and out when I do that, and not just the game. I have 3 monitors and it happens on all three of them. KDE does not do this.
The second issue may be related to the first: sometimes when a program exits from a bad state, the icon in the task bar remains and the only way to get rid of it is to relog. This happens every time I exit Rocksmith if I click the button to close while the screen is blanked or partially blanked, but it's not the only program I've had this happen with. I've also had it happen on two different taskbar panel apps, the default one and one I'll have to go hop on my computer to give you the name of, though when I switched the default taskbar had a couple dead icons and they didn't appear on the new one until the next time.
I'm not on the LTS kernel that ships with Mint, I had to upgrade to the current branch to get my video working.
I've not done much troubleshooting on the second, and my troubleshooting on the first is focused on solving the audio problem as I think the graphical problem will at least not be triggered once that's working right.
I've also had other issues I'm not sure if they're Cinnamon related, Mint related, general Linux related, or hardware/driver related, but I've had issues with the screens not sleeping while the screen is locked, and on a laptop the system not sleeping while on battery. I know suspend is buggy, but I've had it work properly on the same system with MX Linux (dual booting).