Ubuntu boot issues

It says you have UEFI secure boot on, so surprised it boots at all.
BIOS boot should not work with Secure boot on.

You show a bios_grub partition, but formated FAT32 and grub installed to gpt's protective MBR for BIOS boot, but it also says no core.img in the bios_grub partition. So not correctly repaired for BIOS boot.
A bios_grub partition is normally 1 or 2MB unformatted for BIOS boot. It has bios_grub flag.
And an ESP - efi system partition is FAT32 formatted with boot flag. Windows is often 100MB, but we suggest larger like 300MB or more.
It may be possible to have both BIOS & UEFI, but you need both a bios_grub & an ESP as separate partitions.

But your fstab shows a mount of the ESP. So install was UEFI, but without ESP grub did not install in UEFI boot mode.

Which do you prefer UEFI or BIOS? You do need to be consistent and always boot Ubuntu & flash drive installers in the same mode all the time.
Boot-Repair says it was booted in UEFI mode.

I would change sda1 from bios_grub to ESP by changing flag to boot flag with gparted on live installer.
Then use Boot-Repair to install the UEFI version of grub. No need to erase grub in MBR, but it will never work and just give errors if you attempt to boot in BIOS mode.

Since you only have Ubuntu, what brand/model system. Some have no issue booting Ubuntu UEFI entry. Others modify UEFI to only boot Windows entry and we have to do work arounds.