EFI is a bit tricky for people who have installed previously on Legacy boot where everything was straightforward. As the day goes on we keep on seeing more and more computers with EFI boot and worse secure boot.
Needless to say for any computer switch off the secure boot if you want to install Debian. But EFI needs special love during installation. This thread should help document the pitfalls and methods on how to proceed with an EFI installation.