When I did the manual partitoning, I used what I found on this post for uefi systems
specifically this
For uefi
You need to create one 300 mb fat32 partition and mount it as >/boot/efi and flag it with esp and boot
And one btrfs partition mount it as /
One odd thing however is my install shows /boot as a mount point but not /boot/efi. I tried installing with just /boot and I ran into the same grub issue.
The whole it flagging the entire partition as an EFI system is recent, that only happened after I tried to install by “replacing a partition”