My understanding of generic Debian OS installation is as follows:
Installation "live" distribution is booted via bootloader from installation media to memory
Installation procedure starts - in case of Debian it's the DebianInstaller https://wiki.debian.org/DebianInstaller/
Installer guides user using wizard to perform OS installation to a computer ...
I'm scared to remove any other EFI partition because I don't know which one is a grub and which one window boot
Based on your screenshots, you only have one EFI partition in the first place.
Quite possible that either a) you already removed the Ubuntu one, or b) both Windows and Ubuntu are using the same EFI partition.
The EFI partition is just a regular ...
This is exactly the problem we have been facing for a long time in a CIP with dual-boot computers administered remotely.
Unfortunately, I can't come up with a complete solution, just another idea that might help to find a solution: Grub could get either the complete configuration or at least the configuration for "next boot" or/and "default ...
Besides updating the BIOS/UEFI which Dell says to do for that error.
There is another possible cause..
Short answer is.. the error message from Dell's BIOS/UEFI is misleading, it can mean simply can't find bootable ...