For RB2011 to work as CAPsMAN for ax devices or ac devices that supports wifiwave2 drivers you also need to install wifiwave2 package onto your RB2011. Problem is, RB2011 doesn’t support wifiwave2 drivers…
Workaroud is to use one of your devices that have wifiwave2 drivers installed as capsman controller.
But OP have cAP ax, so can replace RB2011 with something like ax3 or maybe RB5009. Then capsman can be used and OP will have newer devices to work with