Big Sur installation installation ending in endless boot loop

[HarWes]

Tried to install Big Sur on an iMac late 2015 with 1 tB SSD-drive. Download is working, installation starts as expected, after chosing the installation drive (only have the MacOS-SSD-drive) installation starts. Two minutes after rebooting (with the progress-line on about 5%) the machine reboots, and reboots, every two minutes.....
Tried already:
- new installation app
- installing form safe mode
- resetting NVRAM (opt-Comm-R-R)
- checking hardware (comm-D)
- removing all old stuff with CleanMyMac X.
Nothing works, I have to start in Recovery mode (comm-R) and re-install Catalina.

Any suggestions?

 

[Mac Hammer Fan]

Had this with 11.0 but not with 11.1. I guess you need the latest version of the installer.

 

[HarWes]

Had this with 11.0 but not with 11.1. I guess you need the latest version of the installer.

Tried it with 11.1 but unfortunately it doesn't work either. Did you change anything else before trying 11.1?

 

[BLUEDOG314]

If you’re backed up just do yourself a favor and do a clean install. I clean installed Catalina and the .4 update and a few months later tried to update to Big Sur and it failed. I think there’s a lot going on with firmware changes initially going to Big Sur that creates more potential points of failure. Clean install from a USB installer is probably the safe bet.

 

[HarWes]

Tnx Bluedog, turned out to be the best choice. Gained a lot of speed and runs smoother than before. Recommend this to everyone updating to BIG SUR.