You can just create another EFI partition for Pop!_OS. That's what I did on my Lenovo ThinkPad X1 Extreme Gen 2 that came preinstalled with Windows 10. I just resized down the Windows C partition to make space and created /home, /boot/efi, / and swap partitions. It worked fine and I can still boot into either Pop!_OS or Win 10. I'm using Pop!_OS mostly now so defaulting to that but I can press F12 at boot to go to EFI boot menu to select Windows 10 if I need it for some reason.
I made the new EFI partition 1 GB.
Here's what my partitions currently look like (I just recently did some changes since I was running out of space on Linux partitions so I resized my Windows partition down a bit more and moved my /home partition there (that's why it's in front of the EFI partition now):