Grub Config Changes with LMDE6 Install / Changes Boot Order of Debian and Slackware:

[oldfred]

Generally when you get a major update to grub, it changes boot order ot make that install the default.
You just then need to manage boot order preference.

You can use efibootmgr to change UEFI boot order.
Or just boot into preferred install & do a "sudo grub-install" which uses all defaults & ESP of entry in fstab.

man efibootmgr
sudo efibootmgr -v # to see current boot order
sudo efibootmgr -o xxxx,yyyy,zzzz #etc to set boot order Some only need one digit, others need all 4.
But HP computers do not seem to work with efibootmgr orfering. Then you have to use HP's system settings.

[UltimateCat]

Yes, Debian and Slackware are each on separate HDD's.
I'll check the fstab files on Debian and LMDE6 for a template. I understand now, to use the correct UUID for the right drive and partition.
Your example is helpful, thank you.

[UltimateCat]

Booted into Debian 12 the output was:

sudo: efibootmgr: command not found

man efibootmgr
No manual entry for efibootmgr

When Slackware and Debian get a new kernel I update-grub in LMDE6 and reboot and all distro's boot w/o fail.

So thinking on what you said, it must have been a major update to Grub that made this happen.
By this I mean the switching of the distro's in the Grub Menu.
That makes sense Oldfred: thank you.

The funny things is for the last 5 years Linux Mint on the nvme always stayed at the very top of the Grub Menu, Debian second and Slackware last in the Menu.
I never had this switching until the installation of LMDE6.

When I understand how manage the boot entries like you do with the 40_custom I'll practice that.
You've been very helpful, thanks.

[UltimateCat]

It's been on thing after another since the new year with getting my desktop and all 3 distro's right.

Finally had success with getting Devuan installed where LMDE6 used to be.
Oh, and btw, since installing Devuan there has not been any more flip flopping of my distro's in the Grub Menu.

I'm slowly but surely getting to the articles you linked for me.

Hope everyone's new year is off to a good start!

[UltimateCat]

Reading Grub 2 Custom Menu's was very helpful, thanks!

I installed Devuan over LMDE6 and the triple booted system run's fine now.