BIErrorDomain error 8.

If you are trying to install Big Sur on a external hard drive, and you get this error, I figured out a way around this, Open the Big Sur installer, and get to the drive selection screen, and make sure the external hard drive is plug in and open disk utility and erase the drive. Make sure Format Mac OS Extended (Journaled) Guid Partion Map, and do that while on the drive selection screen of the big sur installer, and the external drive should become available to install Big Sur on

It worked for me!
But the only difference was that I'd to partition my HDD while on installer screen.

I tried to install Big Sur on my SSD drive and I got this error and it is grey out. It was already formatted Mac OS Extended (Journaled), what else I need to prepare for Big Sur to be installed? Please help. Thanks.

(it is a good thing so far it is not installing on SSD as I read there are lots of bug still, causing many apps not working...but I could installed in another HDD connected to this iMac. This was my original HDD (fusion drive), which was about to install and restart with Big Sur, which could be a saving grace because now I can what is working on HDD and delay the SSD Big Sur installation.)

Please help with to overcome the BIErrorDomain Error 8 and installation on SSD issue. Thanks.

When I tried to download macOS Big Sur on an external usb, I could only get it to work by using GUID partition mapping and APFS unencrypted format, though you will need at least 35gb of free space to download it

I hope this works!

Same as CodyBrooks. Got this error trying to start install on external SSD, only was able to continue after formatting as APFS.