@Retoucher
python DowngradeELF.py --sdk-version 05.050.001 --verbose old.elf new.elf
and
python DowngradeSFO.py --sdk-version 05.050.001 --system-version 05.050.000 --verbose old.sfo new.sfo
that did it for me.
if you run into "ModuleNotFoundError: No module named ..."-error, look at the post by...