Hmm, there's not much to go on. How did you track this hang down to this line? Can you share the log output?

I cloned the repo locally, linked my kernel to the local version and added debug statements. I put 1 statement after the line I linked to and 1 after. Only the first 1 ran. The best photo I can add would be from my phone.

As you can see in the photo it no longer hang. Instead of only copying over the first entry of the old page table, I started copying over all entries and now it works. The panic you can see in the photo seems to be from the fact my system uses huge page table while the bootloader expects 4KiB tables. If you know, could you explain to me why copying over all the old entries would fix it.

The frame buffer (0xfc_1000_0000) address is in the second pml4 entry, interesting. Currently, we only copy the first pml4 entry, but when the bootloader tries to access the frame buffer it needs the second pml4e. The assumption in this comment was incorrect. Your fix (copying more entries) seems reasonable unless maybe that's what's causing the panic below? Freel free to open at PR. I'll investigate some more later this evening.