Well that was weird, I have been having loads of issues with my MX Master 3 for Mac stuttering and lagging and generally being a horrible experience. I have been using it with a unifying receiver plugged into my OWC Thunderbolt (4) Dock, which is sitting about 60cm away under my laptop stand.
Turns out - that’s enough distance and electrical noise to cause the problem. I moved the receiver closer (using a port on my monitor arm) and it works fine now! I generally hate wireless mice, and I’m not really sold on the weight of this one, but finding a fix for my ~$150AUD mouse being a complete arse is nice.