If you faithfully followed the instructions up to this point, you'll be glad to know that you are precisely 3 bugs away from having a working Linux-based system. So, let's get started:

After executing bootm, you may notice some successful loads of the FDT and ramdisk, but the following error during the kernel loading process:

uncompressed: uncompress error -28

Congratulations! The kernel is finally booting. I'm certain you're thankful for keeping that Makefile up to date, right? But what's this?

[    1.878803] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[    1.887072] CPU: 2 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc1-00248-gb6e6cc1f78c7 #1
[    1.894996] Hardware name: TechNexion PICO-PI-8M (DT)
[    1.900051] Call trace:
[    1.902501]  dump_backtrace+0x90/0xe8
[    1.906183]  show_stack+0x18/0x24
[    1.909510]  dump_stack_lvl+0x48/0x60
[    1.913182]  dump_stack+0x18/0x24
[    1.916503]  panic+0x31c/0x378
[    1.919567]  mount_root_generic+0x254/0x324
[    1.923762]  mount_root+0x16c/0x330

First time seeing a kernel panic may be a bit daunting, but the reason looks to be pretty clear:

Unable to mount root fs on unknown-block(0,0)

The kernel needs to know the backing device (and partition) for the root file system in order to mount it at /. Apparently, U-Boot did not know how to tell it to use the ramdisk as rootfs, but chances are that the kernel does know about it.

This is not documented in the command's help message but bootm relies on an environment argument called bootargs to pass the kernel its command line arguments. This should be a good place to start our investigation:

u-boot=> printenv bootargs
bootargs=console=ttymxc0,115200,115200 rdinit=/linuxrc clk_ignore_unused

From rdinit=/linuxrc we notice that the obsolete change_root procedure is being used. Since we don't actually have a persistent rootfs, let's just treat the ramdisk as root.

Now that the kernel panic has been solved, the only remaining issue is a freeze right after forking into User Space. The final kernel log message should be indicative of the underlying problem:

Welcome to Buildroot
buildroot login:
[    9.473402] random: crng init done
[   33.757425] buck1: disabling

Try to decompile the device tree that we include in the FIT image and that is passed to Linux. What is buck1?
Apply the patch mentioned in the tips section below, then recompile the DTB and the FIT image. This should solve the problem.