Bazzite's installer won't allow to set mounting points

Hi! I.m struggling with this installation in an old PC Gamer with a RAID of two SSD. I have readed a bit and have copied the setup of disk and partitions from another installation attempt to this one: - Small FAT32 partition, for bios boot, I think; - 1 GiB ext4 partition for /boot, Bazzite boot; - 444 GiB BTRFS for root of Bazzite that is a RAID of /dev/sda3 and /dev/sdb3 did by mdadm, mounted and formatted by Bazzite's command line. I also rebooted after and the result is the same. Curious fact: the RAID got a "0" instead of md0 or md0p1 that is where it is defined. My motherboard does not have secure boot or UEFI, old school BIOS boot. As long those partitions are listed in the installer, I can't make any operations on it. Options are all gray. There is "format" operation available by the only option is "swap". The "advanced" option is the same: the list of these partitions but I can't assign mounting points to it. What is missing?