Separating EFI partitions of Ubuntu 20.04 and Mac OSX on Macbook Pro
I am not sure why the Ubuntu installer allows the user to select which EFI partition to use, then ignores the setting and installs to the first EFI partition. Below are the step to move the boot files to the second EFI partition.

Boot to Ubuntu.

Press the control+option+T key combination to open a Terminal window.

Enter the command below to become the root user.
sudo bash


Enter the command below to format the second EFI partition.

Note: This command will erase the contents of this partition.

mkfs.vfat -F 32 -n EFI2 /dev/sda3


Enter the command below to mount the second EFI partition.
mkdir efi2
mount -t vfat /dev/sda3 efi2


Enter the commands below to copy the boot files from the first EFI partition to the second EFI partition.
mkdir efi2/EFI
mv /boot/efi/EFI/BOOT efi2/EFI
mv /boot/efi/EFI/ubuntu efi2/EFI


Enter the commands below to get the UUID of the two EFI partitions.
blkid /dev/sda1
blkid /dev/sda3


Edit the /etc/fstab file to change the UUID value for the mount point /boot/efi. This can be accomplished by replacing the UUID of the first EFI partition with the UUID of the second EFI partition. Below is the command to open the file in the nano editor.
nano /etc/fstab


Enter the command given below to output the contents of the /etc/fstab file. Visually confirm the changes to the file.
cat /etc/fstab


Enter the command given below to unmount the second EFI partition.
umount efi2
rmdir efi2


Enter the commands given below to close the Terminal window.
exit
exit


Restart the Mac.