So I just got myself a nice new ergonomic mouse with 7 buttons. However, four of the buttons are defaulted to options like forward/back/home/etc with no option to change it to a simple button click through the software it came with. So how did I take control of these buttons? I'll tell you, because I couldn't find any easy solutions on the web.
Step one: Buy a mouse. I got a cheap-ish JLAB ergonomic mouse. 7 buttons, super comfortable.
Step two: Download the mouse software, Karabiner, and BetterMouse.
Step three: Through the mouse software, set the buttons you want to a letter or number. I set the ones that weren't listening to 3, 4, 5, 6. Then delete that, never use it again.
Step four: Through Karabiner, in the simple modifications section you can then tell it to take any input from that mouse and assign a button-# to it, so set the letters you picked to the button number you want. Use Karabiner Event Viewer to confirm the changes.
Step four: BetterMouse will now recognize your clicks and you can set them to do whatever you want in the OS, or by program.
Karabiner is free, but BetterMouse is paid. There might be another option I'm unaware of, but I think BetterMouse is a solid buy for $10.
Now I need to decide what macros I want to attach to my 2 new buttons.