Macbook slow boot/no switch off - boot-info enclosed

Question

Just installed Ubuntu 20.10 on a 2007 Macbook3,1 (4GB memory, 80 GB HDD) No install issues, all works fine, except :

• very slow boot
• manual switch off (Mac freezes)

I corrected a MOKLIST message at boot time with that :

-sudo su - -cd /boot/efi/EFI/ubuntu -cp grubx64.efi shimx64.efi -reboot

as mentionend in Ubuntu 20.04 Failed to Set MokListRT: Invallid Parameter

Boot-info shows some errors: https://paste.ubuntu.com/p/Xrh6FRdQGk/

Is there a way to solve this boot/switch off issue ?

thanks for your help,

Bibif