I wanted to give a final update on this.

Following Dennis's suggestion to put the DTB on the EFI partition of the internal NVMe drive fixed issue number 1 for me. Issue number 2 was that my Intel Optane NVMe drive in my external USB-C enclosure was not working with Fedora on the X13s (but it works on x86 computers I have). I swapped it out for a Silicon Power NVMe drive and now it works! The GNOME desktop environment loads up with the latest Fedora Workstation 40/Rawhide builds. No more black screen!

I've also been trying out the Fedora Asahi Remix on my MacBook Pro and, yes, I must say it is a much smoother experience than the Lenovo Thinkpad X13s so far. I thought the lack of the latest OpenGL and no Vulkan would be a deal breaker but most apps work great.

Sincerely,

    Luke Short