Comment 4 for bug 1966621

Your description definitely reads as if you are confusing /boot (where the kernel and initramfs go) and /boot/efi (where grub goes, to be read by the system firmware).

You should be able to select "Use as boot disk" from the actions for the disk when it has an existing ESP (and this will be done by default if any partition from this disk is selected to be mounted). If you can't do that can you extract the /var/log/installer/block directory? (If you're using a USB stick to install it will be stored on the USB stick in the 'writable' partition).