However, in that case Magisk should have recognized that the given img file cannot be patched and should have printed an error (did you watch what Magisk wrote when patching!) - but there should be also no patched img then
I do not patch img, i install gsi-img over stockrom. And then, I made a backup of boot partition with TWRP. This file I used for patching with DeltaMagisk.
This patched boot partition file do not work
Now, to un-brick, you should try to dirty-flash the ROM again, it should fix your Boot partition
I do not have to make a dirty flash. I restore unpatched boot from TWRP and device does boot.
Generally, System and Boot are different partitions and flashing System image to Boot partition is a way to brick the phone
Do GSI-Images only modify system partition, do they not contain boot partition?
If yes, boot-partition is part of stock rom, not GSI-Image part, right?
As far as i know, Magisk and DeltaMagisk only modify boot partition.
When I flash stockrom without GSI, DeltaMagisk can modify boot partition and device can boot.
When flashed GSI, it should be still the same boot partition. But when I modify boot partition the same way, device doesnt boot.
So i suppose there is a problem with GSI
When using official magisk, there is a notice that for GSI-Images you have to use a special version:
Magisk fork with some addition needed for phh-treble gsis. - Magisk-Phh
As you can see, the main developer of GSI/TrebleDroid, Phh, made the last version 2 years ago. Now he is retired in that project.
I suppose, he never made a modified Delta-Magisk version.
So it would be kindly if HuskyDG makes a Version working with GSI-Images.