A recent change to the postmarketos-mkinitfs package in 1.4.1-r5 causes the initramfs to be built without support for the ascii NLS in the kernel, which is required for the fat32 file system used in EFI boot. Since the Pinephone Pro uses EFI boot now, this broke booting on this platform.
...
EFI stub: ERROR: FIRMWARE BUG: kernel image not aligned on 64k boundary
...
Mount boot partition (/dev/mmcblk0p1) to /boot (read-only)
Detected vfat filesystem
[ 3.680320] FAT-fs (mmcblk0p1): IO charset ascii not found
mount: mounting /dev/mmcblk0p1 on /boot failed: Invalid argument
ERROR: initramfs-extra not found!
This will be fixed in postmarketos-mkinitfs-1.4.1-r7. In the meantime, if you have already upgraded to postmarketos-mkinitfs-1.4.1-r5 or -r6, do not reboot until the 1.4.1-r7 is available/installed on your device.
If you have already rebooted, you can recover the system by booting the Pinephone Pro into jump drive, mounting the /boot partition on your host system, and copying the initramfs file from here to the partition, overwriting the existing initramfs file.
The sha256 checksum for this initramfs file is:
initramfs 6bde0e6fdc383829e0c94cc46ce2b93d17c11214cfc6f301ac6d6d686eceed04