Tearing quotes and stuff out of “Flying Guns of World War II; Development of Aircraft guns, ammunition, and installations 1933-1945” by Anthony G. Williams and Emmanuel Gustin.
"The Luftwaffe saw considerable variations in belt loading, as follows:
The 7.92mm MG-17 used in fighters were loaded with 50 percent AP, 40 percent API and 10 percent HEI (a Beobachtungsgeschoss, or observation round, which exploded on impact to show the pilot he was on target). For ground attack and for the MG-15 and MG-81 felxible guns, the sequence typically changed to equal proportions of AP, AP-T and API; v-munition loadings were only used in the MG-17. The 13mm MG-131 was loaded with one or two HEI for every AP/T. Official loadings for the 20mm belts and magazines varied at different times and places. Three types of projectiles were usually mixed in the belts: HEI (M-Geschoss), HE/T and AP/API or APHE. Ratios quoted include 1:1:1, 3:1:1, and 2:2:1 respectively.
Generally speaking, the more powerful weapons were able to provide sufficient destructive power with only one or two projectile types, so belts were less varied. As we have seen, an equal mix of HEI and SAPI became standard in the RAF’s 20mm Hispanos, whereas the 30mm MK-108 principally relied on the M-Geschoss HEI it was designed for. The .50 in Browning fighter belts in US service started the war loaded with 40 percent AP, 40 percent Incendiary and 20 percent tracer. The tracer fell out of favour when it was realised that it was providing more help to the enemy. By the end of the war, fighters were primarily loaded with the M8 API (which appeared in service in spring 1944), as this proved to be a good general-purpose projectile, although the M23 incendiary also saw some use."
So overall, the luftwaffe was using high explosives for their cannons. I have no clue why you want to go “Mmmm But do it with AP!” as if they ran full AP against bombers for some reason. Sounds like you’re moving the goal post.