The only aircraft currently stored at EDI is a Norwegian B737max and that's not out of choice.
Jet2 have four based B738s and usually operate less than one return flight per day per aircraft. By basing four aircraft it means that each can fly several times per week which saves the costs of maintenance that would be necessary if some of these airframes were put into storage.
easyJet and Ryanair both have eight based aircraft and Loganair has three. They also have lots of slack in their schedules but this arrangement keeps all these aicraft airworthy and gives plenty of cover for delays and any aircraft that goes unserviceable.
I reckon there are about ten more aircraft based at EDI than are needed to operate all of the currently scheduled flights but none are in storage because they all fly regularly, albeit at much lower utilisation rates than they did pre-COVID-19.