Which file format support for installing RHEL 8 for /boot/efi while / in LVM?

RHEL 8 supports UEFI in Secure Boot enabled as well as with Disabled mode. That is a very good change, as Most of the new machines only support UEFI mode. But while installing RHEL 8 with UEFI mode, why in custom partition; I had to choose both * /boot in standard partition * /boot/efi The Custom partition wold looks like this

/                LVM 
/boot            Standard
/boot/efi        
/swap            LVM

Why not only /boot/efi works ? I tried going with /boot/efi in different file formats, removing /boot. But every time it says format not supported. Now I am stuck with this question help me understand this.