shim-signed not working on MacOS Catalina

Hi,

i am using a MBP 2020 with Ubuntu.

I am trying to enabled Secure Boot (for now only refind without SIP and Secure Boot is working really fine). If i try to use any signed version of shim on my system is not booting and it is always starting in recovery mode. If i try the Windows or Mac OS Bootloader with Medium Security, everything is fine.

Can someone tell me how to debug this?
If i only use the shimx64.efi with no bootloader like grubx64.efi there is no output just the recovery mode. Is this right or should there be any other output?

Thanks a lot.

Cu kami83