One feature that annoys the heck out of me on my MX Master is horizontal scroll. While usefulness of the horizontal scroll itself is already debatable, its positioning on MX Master is abhorrent. Side scroll wheels are extremely easy to hit by accident and they turn as soon as you even think about them. The only saving grace is that most applications don't support them.
Under Windows, it's easy to disable them in Logitech Options software. But Linux has no equivalent of this (and yes, I'm discounting LogiOps here, potentially unfairly so). Fortunately, Linux does offer a fine-grained control by default.
The first step is finding mouse ID under pointer devices (ignore it under keyboard).
To verify you have the correct mouse and if you want to check which buttons horizontal scrool wheel occupies, you can use
xinput test <id>
For MX master (and honestly pretty much any other mouse I tried), these values were 6 and 7. Thus we can simply disable them using
xinput set-button-map <id> 1 2 3 4 5 0 0 8 9
And that has our horizontal scroll gone for good. Interestingly, while we can still see motion values, no application seems to react to those alone.
As this change will dissapear with reboot, I personally place them in
.bash_profile so they get applied each time my user logs on.
PS: I also have my thumb button reconfigured.