I'm shocked how little information there is on this online, I ended up ordering an entire new scroll wheel when I didn't realize that was entirely unnecessary, the switch for the middle mouse button is a little copper plate at the top of the board. For me all I had to do was clean it off with a bit of alcohol on a swab and it works like brand new again, granted my mouse is only 2 years old and I was pretty annoyed when it started having issues this early...
I would recommend ordering new feet for the mouse (they cost around $2 on aliexpress) and no heat gun was really necessary to remove them, just a plastic pick/spudger. If after cleaning the switch with a swab you see the button still doesn't function properly or if you find that the switch is completely broken I would recommend just looking for an entire new board, from what I saw you canstill find them for about ~25% of the price of a brand new mouse (but don't quote me) so still worth it if you ask me.
The disassembly guide is pretty good but the only things I would do is add a guide specifically for fixing the middle mouse button as at least for me it's a very common issue with logitech mice (this is my third logitech mouse displaying this behavior) and also i would remove the part about needing a heat gun and highly recommend people buy new feet for the mouse, trying to peel off the old ones perfectly so you can reuse them (or glue them back on) is insanity, just spend the $2 on new feet.