I don’t think you can default boot to Android (but it should be possible I guess by modifying the bootloader config).
You have a reboot to eMMC (= android) button in Kodi power menu.
Note that it does not appear in -NG if you’re still on Android 12, but you can patch the skin on NG if you want it (see Reboot to eMMC/NAND is missing from Estuary Skin - #4 by fthiery)