1. Verify that the EFI partition is on slice 1 by running the following command:

diskutil list

2021-03-01T10:56:27-08:00:=================diskutil list=================
2021-03-01T10:56:27-08:00:/dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *2.0 TB disk0
1: EFI ⁨EFI⁩ 314.6 MB disk0s1
2: Apple_APFS ⁨Container disk1⁩ 1.3 TB disk0s2
3: Microsoft Basic Data ⁨Windows⁩ 700.3 GB disk0s3

(note that the EFI partition is disk0s1).

  1. Verify that the EFI partition can be mounted by running this command in Terminal as an Admin:

sudo diskutil mount disk0s1

(if your bootcamp partition is on a disk different from disk0, adjust the command above accordingly)

If the EFI partition cannot be mounted, then either the disk is not GPT formatted or the EFI partition is corrupt. This can be fixed by completely erasing the drive and formatting as GPT. NOTE: THIS WILL DELETE ALL DATA ON THE VOLUME INCLUDING ANY MAC PARTITIONS.

If the EFI partition is not on slice 1, then the disk was probably formatted with Windows utilities. This can be fixed by completely erasing the drive in Disk Utility and formatting as GPT. NOTE: THIS WILL DELETE ALL DATA ON THE VOLUME INCLUDING ANY MAC PARTITIONS.