Just to be sure this is not a UX issue:
did you click on the down arrow? (not the grey/orange effect toggle)
Can you try the following?
* download the attached effect units configuration
* put that into your .mixxx folder
(ususally in Home, dunno what it is called in Arch)
* start Mixxx
Are the effect sots loaded now?
Can you change effects?
Just to be sure this is not a UX issue:
did you click on the down arrow? (not the grey/orange effect toggle)
Can you try the following?
* download the attached effect units configuration
* put that into your .mixxx folder
(ususally in Home, dunno what it is called in Arch)
* start Mixxx
Are the effect sots loaded now?
Can you change effects?