As an expérimentation, is it possible that an advanced user, please make this test :
Take a device running an updated Stock Android.11 firmware,
and install e-Q on it !
Flash a TWRP if possible,
Reboot to recovery
Change /vendor.IMG to an older, ( extracted from a s Stock Android.10 firmware )
Format /data, reboot to recovery,
Wipe /data /system /cache /davilk-cache,
Install /e/-0.17-Q or /e/-0.18-Q
Thanks in advance.
That is what the easy installer seems to do for installing e-oreo.8 over Stock Android.10 on the Samsung s9/s9+