Help for dual booting THINKPAD C13 (MORPHIUS)

Hello, some time ago I bought a THINKPAD C13 chromebook(AMD Ryzen 5 3500C - 8gb) (MORPHIUS) to install linux. However after trying chrome OS for a while I found out it’s very useful for me the ability to run android apps.
So now I want to try dual booting. After a lot of reading, I turned on developer mode and successfully installed Legacy Firmware following the instructions.
But I wasn’t able to boot from a bootable USB to install some distro.
I always used debian based distros, I use MX linux for quite a long time and it’s fine for me, so I burned a USB through MX OS choosing latest ahs option (with 6.6 kernel) because I think I read somewhere 6.1 is not supported.
The welcome menu opens but it doesn’t boot.
Then I tried burning USB with Rufus on windows and choosing mbr instead of GPT (not sure if it’s enough for legacy compatibility though)
I had the same result, not booting.
Am I missing something? Is the distro incompatible or what?
Is it a GRUB problem?
Do I have to enable somehow(?) iommu=pt boot parameter?
Also I’m confused, am I supposed to do the partitioning through the distro installation as usual or somehow before, because I understand it’s not safe to mess with partitions in chrome OS.
Is Gparted supposed to work in crostini ?(it didn’t for me)
Any other distro proposal for dual booting?
I forgot to mention I upgraded the SSD to 512 GB
Thanks in advance!

  1. I have had more luck with UEFI than the RW Legacy firmware on this machine for running Linux, but I have only run Fedora, Debian, openSUSE and Submarine.
  2. My knowledge may be limited here, but I do believe it may be difficult to dual-boot ChromeOS and Linux since ChromeOS has so many different partitions and quite the complex setup to make the stateless updates work flawlessly, you may be better off just installing Linux