You will see old forum posts recommending Reicast. Avoid it. Reicast was abandoned in 2018. It does not work well on modern Android versions (12/13/14), and it lacks the Windows CE support that Demul users expect. Both Redream and Flycast have surpassed it completely.
If you want the true open-source successor to Demul, Flycast is your answer. Flycast is a fork of the original nullDC and Demul codebases, merged into a single, actively developed core. demul emulator android
Arcade platforms (Naomi / Atomiswave / Chihiro) You will see old forum posts recommending Reicast
Running Demul’s Windows build on Android Arcade platforms (Naomi / Atomiswave / Chihiro)
Just because Demul isn't on Android doesn't mean the experience is dead. Two major emulators currently dominate the Sega ecosystem on mobile. Depending on why you wanted Demul, one of these will be your perfect match.