Hello Jan,
the installation of a device-tree using argument EFI_DT_INSTALL_TABLE
has been removed from the EFI_DT_FIXUP_PROTOCOL specification on
2021-02-06. It still exists in U-Boot but efibootguard should not rely
on this deprecated feature.
Cf.
https://github.com/U-Boot-EFI/EFI_DT_FIXUP_PROTOCOL
Please, consider updating function replace_fdt() accordingly.
Best regards
Heinrich