Seem that I have the same problem. Sadly wont help much, because I tried pretty much same things. I also did upgrade BIOS (Gigabyte X870 EAGLE WIFI7). After that everything worked, but when I installed system updates, I was stuck on boot - black screen after Grub. I fresh installed CachyOS with limine this time, but still same - only cachyos-lts can boot.
CPU: AMD Ryzen 7 9800X3D
RAM: Kingston FURY 64GB KIT DDR5 6000MT/s CL30 Beast Black EXPO
Are you booting from a NVME drive? Because this seems to by my issue and yet I believe my problem is a slightly different one because I get a Kernel Panic, not just a freezing boot process… Still, this is a very sad situation at the moment because I am now stuck with a pinned Kernel and I am running out of ideas 
So I’ve spent a while over time compiling some kernels and while I’m not sure exactly the procedure for reporting things, it appears that 789a5913b29c2558a4a80b8740a2523f75285507 iommu/amd: Use the generic iommu page table (Nov. 4 2025) is the kernel commit that’s the source of the problems.
It does check out that it easily could be, although it’s also one that’s mostly just turning on stuff that was prepped before.
I can confirm this has also happened to me on the exact same setup as OP. But mine was with my B650 Aorus Elite AX bios update (Bios: FC3) worked on (Bios: FB7) too scared to downgrade my bios firmware incase it bricks. It hangs at the splash screen when booting up LTS did work until I updated drives then boom same thing happened. Any ETA on a fix for this?
Problem disappeared for me after recent update. I’m now able to boot Kernel: Linux 6.19.5-3-cachyos