When I try to install onto the existing LVM logical volumes for / and /home, I have a separate (unencrypted, no-LVM) partition of 500 MB for boot on /dev/nvme0n1p1 (LVM is on /dev/nvme0n1p2).
However, the pull down-menu for “Install the boot loader on:” gives me only a choice of the Master Boot Record of the full disk (/dev/nvme0n1), not the 500 MB partition. Maybe that is the reason for the grub-install error (it still persists).