Multi boot system but no Grub Menu

[dragonfly41]

It might help understanding if OP boots up LiveUSB, Try UBuntu, runs gparted, and reports what is seen in each of the three OS partitions, in particular EFI partitions.

[yancek]

OP has said a few times now It boots straight to Ubuntu, But you know how that goes.

The boot repair output in the first post indicates that Ubuntu on sda3 is the default but the first direct mention by the OP that it is in fact booting Ubuntu was post 36. Although asked and never answered, were the modifications/edits done in Ubuntu?

It might help understanding if OP boots up LiveUSB, Try UBuntu, runs gparted, and reports what is seen in each of the three OS partitions, in particular EFI partitions.

All that information is in the boot repair output in the initial post and all 3 OS's are on the same drive with only one EFI partition. It also indicates the grub.cfg file on that EFI partition is pointing to Ubuntu on sda3. Also shown are the Hidden option in the /etc/default/grub file of Zorin and the saved option in the same file on Mint. I don't believe those are default settings. Booting into Ubuntu and making the edits there should have resolved the problems but it is an unknown if that was done or what other changes may have been made.

[dragonfly41]

I see ..

and all 3 OS's are on the same drive with only one EFI partition.

.
Just an observation .. I have triple boot setup and I make a point at LiveUSB time of creating a unique EFI partition for each OS (on a partition or separate SSD in external docking bay/caddy). And also in each EFI partition I install rEFInd. I know that this redundancy isn't necessary and one EFI partition will suffice.

[SUPERFITTER]

me@me1:~$ efibootmgr
BootCurrent: 0001
Timeout: 3 seconds
BootOrder: 0003,0002,0000,0001
Boot0000* EFI DVD/CDROM
Boot0001* OsLoader0000
Boot0002* ubuntu
Boot0003* rEFInd Boot Manager
me@me1:~$

[1fallen]

EDIT: I'll assume you now have good back-ups in place before proceeding with my suggestions below.

This should get you to Ubuntu first, and then as a second option shows rEFInd

 sudo efibootmgr -o 0002 0003

Now reboot, Do you now have a Grub menu?

I have not seen an entry like you now show>>>"Boot0001* OsLoader0000"

[SUPERFITTER]

1fallen

Sorry no Grub menu, straight into Ubuntu.

[dragonfly41]

When you reboot and immediately go into BIOS (hit F2 ??) what options do you see in boot order?
Any other settings in there report back.

[SUPERFITTER]

My BIOS

[1fallen]

That Picture is way to small for my aging eyes

Do you have a boot priority with F12 when immediately booting up? (Spam your F12 when it first begins to restart)

EDIT I did see First Boot device is a USB drive, not what we want though.

[dragonfly41]

+1 "That Picture is way to small for my aging eyes"

Take time to write it down for old codgers like me.