The minimum size will do, and don't worry you can delete later. Create an internal bootcamp partition on your Mac device.This is pretty straightforward, just download the update and select the partition as the install destination. Then I installed macOS Big Sur on the APFS partition.So, in Disk Utility I created a GUID Partition Map and and formatted the windows half as exFAT and the macOS as APFS. It's up to you how you want to do this, but in my case I wanted a 500gb macOS partition and a 500gb windows.Sorry - I'm not saying there isn't a free workaround out there, but I wasted hours of blood sweat and tears trying to avoid it. I wanted to be able to plug it into either my MBP or iMac and have it work seamlessly.I wanted to split the SSD into two 500gb partitions and use it as a boot drive, one for macOS Big Sur and one for Windows 10 ( Home edition, not that windows to go crap).
It specifically says it doesn't support bootcamp ( lies!) I bought a Sabrent ROCKET XTRM 1TB TLC NVMe SSD.I have a mid 2017 iMac with a fusion drive and a mid 2017 MBP.It took me an entire weekend to figure this out and most places I looked said it couldn't be done. I'm writing this to hopefully help anyone who finds themselves in my position in the future.
