Hello, I have installed MacOS BigSur public beta. But today I got MacOS Catalina 10.15.6 as an update.. I have accidentally hit update on the notification bar and realized it is supposed to be BigSur 11 instead of Catalina 10.15.6.  the system restarted and I saw an Apple logo with the loading bar. After that I’m stuck at blank screen forever. After 2 hours I lost my patience and did a force restart. I’m still getting blank screen at startup. I have tried resetting the NVRAM, SMC, tried to boot in safe mode also in recovery mode. But nothing works I’m still seeing blank screen.  I talked with Apple customer care and they are suggesting booking an appointment and they might clean install the OS but I don’t want to lose my data. I don’t have the backup.  can anyone help me to recover the data or fix the boot issue? Thanks in advance