Boot/Grub/Dual boot issue

So as of last night I had a fully operational Mint installation. I wanted to get back to Endeavouros so installed the most current version choosing Plasma this time. After rebooting I have only the Endeavouros listed in start. I attempted several of the posts I could find without success to correct the issue. When I installed I used the option to install alongside the Mint copy. What will I need to provide to determine the issue? Which logs? It’s been a bit but would like both operational but I struggle with the commands need. Not sure if there is a better place to address this. I know there have been several changes in recent weeks.

Did you choose grub or systemd-boot while installing?

I believe it only offered Grub2. How can I determine which it might be?

You may have installed in legacy mode. If your other OS is in EFI mode, that would explain why they can’t see each other.

What does findmnt --real show?

TARGET                                               SOURCE    FSTYPE OPTIONS
/                                                    /dev/sda4 ext4   rw,noatime
└─/run/media/sc/7efd66fa-023c-4ef7-ad27-c1d55ac7ae49 /dev/sda3 ext4   rw,nosuid,nodev,relatime,errors=remount-

Yes. That appears to be exactly what happened. You installed in legacy/bios mode.