Already answered this evening in the “prioritising retail sales over Motability” thread.
In summary, yes dealers get a fixed handling fee. It used to be around £150 but it went up during the pandemic to (if I recall correctly) around £220. However, this is only part of the story. Cars ordered for Motability customers also count towards various volume bonus schemes (which are worth many thousands of pounds), so that’s why people should never believe a dealer that tells you that they only get a tiny handling fee and nothing else. It also explains why some dealers will offer additional discounts off the AP.