Hi.
Same problem here. I cannot mount EFI partitions.
In terminal I have this...
sudo mount -t msdos /dev/disk0s1 /Volumes/EFI
Executing: /usr/bin/kmutil load -p /System/Library/Extensions/msdosfs.kext
mount_msdos: /dev/disk0s1 on /Volumes/efi: Operation not supported by device
mount: /Volumes/efi failed with 71
...
Luckily I have a second disc with Catalina where it still works.
Could you solve it yet?