Is there a way to make Logitech side mouse buttons just be generic mouse buttons?
It turns out that if you uninstall or disable Logi Options in the System Preferences, then at least two of the side buttons on Logitech mice seem to appear as standard mouse events. I.e., Mouse Button 4 and Mouse Button 5.
Having Logi Options configured to do Input Monitoring in System Preferences, which is required for Logi Options to work, blocks apps from seeing Mouse Button 4 and Mouse Button 5 events. And Logi Options itself has no option to just let these events pass through Logi Options unmolested.