Here's what worked for me. I had an existing unallocated 1000MB available on /dev/sda. My ESP was on /dev/sda1 and was 100MB Fat32. I booted into a live linux environment via USB (/dev/sdb) and loaded gparted.

In gparted, I see the /dev/sda with all the partitions. I selected /dev/sda1 then choose copy to the unallocated 1000MB partion and selected to resize to 500MB, appied the changes, the copy completed.

Next, I modified the flags and removed the esp and boot from the old ESP partition and changed it to msftdata. Then modified the flags on the newly created ESP partition, unselecting msftdata and checking on the efi and boot flags. Applied the changes and rebooted, and windows recognized the boot, but still not complete, as the 100mb partition appears as 'system' when looking at it Windows Disk Manager.

I wanted to delete the 100mb empty partition (probably don't have to), so I loaded EasyUEFI and was able to back up the old and the new ESP partitions.

It was working, but since the 100MB old partition was still being recognized as 'system' in Windows Disk Manager and using it. Loaded EasyUEFI, chose the Rebuild Windows System partition option, select the boot partition (C: drive) and the system partition (esp), and it will rebuild correctly. Windows was then recognizing the 500MB partition as ESP Boot System and Windows 10 boots up correctly. I was able to delete the 100MB old partition. You might be able to do the same thing without using EasyUEFI via command line, but this was quicker and easier.

Here's what worked for me. I had an existing unallocated 1000MB available on /dev/sda. My ESP was on /dev/sda1 and was 100MB Fat32. I booted into a live linux environment via USB (/dev/sdb) and loaded gparted.

In gparted, I see the /dev/sda with all the partitions. I selected /dev/sda1 then choose copy to the unallocated 1000MB partition and selected to resize to 500MB, applied the changes, the copy completed.

Next, I modified the flags and removed the esp and boot from the old ESP partition and changed it to msftdata. Then modified the flags on the newly created ESP partition, unselecting msftdata and checking on the efi and boot flags. Applied the changes and rebooted, and windows recognized the boot, but still not complete, as the 100MB partition appears as 'system' when looking at it Windows Disk Manager.

I wanted to delete the 100MB empty partition (probably don't have to), so I loaded EasyUEFI and was able to back up the old and the new ESP partitions.

It was working, but since the 100MB old partition was still being recognized as 'system' in Windows Disk Manager and using it. Loaded EasyUEFI, chose the Rebuild Windows System partition option, select the boot partition (C: drive) and the system partition (esp), and it will rebuild correctly. Windows was then recognizing the 500MB partition as ESP Boot System and Windows 10 boots up correctly. I was able to delete the 100MB old partition. You might be able to do the same thing without using EasyUEFI via command line, but this was quicker and easier.