dwm does not recognise mouse buttons above Button5

[bakkeby]

This does not have anything to do with dwm, but that only buttons 1 through 5 are defined in X11:

https://code.woboq.org/qt5/include/X11/X.h.html#255

You can define these yourself in config.h:

#define Button6 6
#define Button7 7
#define Button8 8
#define Button9 9

or alternatively simply use the button numbers directly rather than the macro in your configuration.

(these macros are predefined in dwm-flexipatch)