Boot problems are really tricky to fix on the computer that’s having them.
If any of your other OS’s still boot, then use them to download a live ISO of your preferred linux distro, and write it to a USB stick.
Then you can diagnose the problem using a new boot environment that doesn’t rely on the main disk.
If the Debians you installed weren’t Live ISOs, then I recommend Arch or Artix for CLI, and Manjaro or Ubuntu for GUI.
You’ll have to mount the drives,
chroot
into the one on the drive that has the EFI partition, thengrub-install
andgrub-mkconfig
into the EFI partition.