Cannot resize APFS container after updating to Big Sur
Finally found a fix! Deleting snapshots using tmutil didn't work but I deleted them with diskutil from Recovery:  diskutil apfs listSnapshots &lt;Macintosh HD's disk id&gt; and then diskutil apfs deleteSnapshot &lt;disk id&gt; -uuid &lt;snapshot uuid from the previous command&gt; for every snapshot. I had 3, two of them were deleted and one returned &quot;insufficient privileges&quot; but it doesn't matter, now everything works. Do it at your own risk, I don't know whether it will work on your Mac.