Maybe some other HC4 owner can chime in and confirm or deny the incompatibility as well. If it’s just me on a wild goose chase, it would be different to the HC4 in general being useless with DietPi 9.8.
Also, I want to reiterate that I would be open to ripping out Petitboot and do whatever it takes to get something better into the SPI.
The thread here started in the right direction, but unfortunately, it died down.
I also agree 100% with @MichaIng 's assessment of Petitboot in the quoted tutorial.
Except that I’m very happy that he spent the time to make Petitboot work at least with the N2+. This is what brought me to DietPi. The Armbian guys just nuke Petitboot and essentially say: Deal with the consequences. This is not what I want.
Ideally, I would like to see just uboot running from SPI, as close to upstream as possible. The ability to boot from USB and SSD and to reboot without interference would be enough.
If you need assistance for test runs etc., I can test for you. I have an M1, N2+ and the HC4 for different environments which all include SPI.