Thanks for the friendly reply 
That information was not present to me at the last update. However, I do not have the microcode line (ALL_microcode=(/boot/*-ucode.img) in /etc/mkinitcpio.d/linux67.preset) and the microcode is loaded just fine (can be observed by this command: journalctl -k --grep=microcode).
To get a common ground for everyone here from the discussion you shown before regarding this Forum entry: [Unstable Update] March 2024 Edition - #33 by koshikas
→ Before, it was discussed in the Arch-Forum:
It rather seemed to be a misplacement of the GRUB_EARLY_INITRD_LINUX_STOCK="" -line. As you see in the posts before, it was at an earlier state called. I would assume(!) that the early position overwrote a latter one, which lead to issues.
Also, it seems not to be necessary, as shown by this discussion of this merge request, which was discussed in the unstable forum: