Using the downloaded Clover r1943 did not work, so I am going to build a new custom Clover 1945. I don't expect that to make the ESP on the Mac drive be recognized either, but opening the case is so much work, ANY software solution is worth a try.

It is very annoying to take such a big step backward, considering that I previously had Clover running successfully.

This is possibly an undocumented limitation of the UD7, or the Chipset, or the controller, where only some ports of some SATA controllers are recognized as bootable UEFI devices. However, the Mac drive is on the same SATA controller as the Windows boot drive, and disconnecting the Windows drive does not help.

The Mac drive is currently on Bus Number 5, Target Id 0 Lun 0. The “Friendly name” is ATA ST1000DM003-1CH1 SCSI Disk Device. The SATA controller is Intel C600 Series Chipset SATA RAID Controller.