I had the same. Installation got stuck at the final stage (status bar) at 50%. After a while, I've got a blinking question mark with a folder icon...so I did the reboot and the status bar got stuck again at 50%, this time no blinking icon. I left my MacBook pro (early 2015) for the whole night but the bar didn't move at all Then, what I did: reboot, again the same status stuck NVRAM reset, no improvement PRAM reset, no improvement Safe boot with SHIFT, didn't work at all Recovery mode - interesting here, it went to the INTERNET recovery mode and not the standard one. In the internet recovery mode, I could not find my disk I used Bootcamp to start windows and luckily with paragon software I was able to mount my mac drive and make the backup of the data Next I made again PRAM reset, making sure it was done correctly After this, the Installation was completed immediately and I could see the login screen of Big Sur Huge relieve! Big Sur works much better on my mac than Catalina. Fans are engaging less, performance is great, and overall very happy with the new system. My recommendation, make sure you make NVRAM and PRAM reboot correctly, you can eventually run the system in verbose mode and see what is the exact error. Try a few times reboot before you pull the trigger on erasing the data and making a clean install. Time machine backup is a must before trying the update. good luck!