Ok, and your efibootmgr output shows:
BootCurrent: 0001 [...] Boot0001* ubuntu HD(2,GPT,97bd7694-b600-487f-a866-7694c80b6ead,0xfa000,0x32000)/File(\EFI\ubuntu\shimx64.efi)
So in fact, the shim package is correctly installed, is correctly installed to the ESP, and is correctly registered with the firmware.
So it's currently unclear to me why this system is failing to boot when SecureBoot is enabled. And I don't think reinstalling 19.04 will help you any.
Ok, and your efibootmgr output shows:
BootCurrent: 0001 97bd7694- b600-487f- a866-7694c80b6e ad,0xfa000, 0x32000) /File(\ EFI\ubuntu\ shimx64. efi)
[...]
Boot0001* ubuntu HD(2,GPT,
So in fact, the shim package is correctly installed, is correctly installed to the ESP, and is correctly registered with the firmware.
So it's currently unclear to me why this system is failing to boot when SecureBoot is enabled. And I don't think reinstalling 19.04 will help you any.