Installed Big Sur on my mac laptop yesterday with its ludicrous 35Gb free space requirement for its monstrous bloat-ware.
After all I had nothing better to do, than to start a quest to free up the required room. I used GrandPerspective, a file space visualisation tool to see where there was unexpected opportunities. I painfully deleted caches and applications but eventually after much deliberating the space was won.
I also moved the install file to a secondary disk and installed from there.
Big Sur looks pretty attractive but I certainly think Apple needs to rethink how it does support installations in the future. They are hardly generous with disk space sizes.