Hi guys, my iMac5k 27'' cant handle startup after I upgraded to Big Sur. I always get stuck with the black screen, the apple logo and a quarterly filled progress bar. I have this since friday and let the machine work over night and get no progress. The Safe Mode works fine, I can restart the system and start in safe mode. But after restart in normal mode I again see the black startup / hanging screen. The NVRAM cleanup startup works fine, too. But afterwards with the next start I get stuck in the startup screen again. I already started the update again in safe mode and get stuck back in apple black screen without progress from about 25%. What can I do more? Thanks