Hey don't know if you still have this issue or not. I just bought a 13600k with an Asus Z690-A ROG Strix (no 12th gen cpu lying around) and has been having a dilemma with updating BIOS too (because Asus recommends you update the Intel ME firmware BEFORE updating BIOS to version 2103 - which is impossible for me without a system already operating). This thread of yours fills me with dread now. haha
However, from my scraping through ASUS ROG forum, for people using 13th gen cpu on Z690 mobo, even if you flash (via bios flashback) your BIOS to the latest version, you might run into issue of system not recognizing the M.2_1 slot. Perhaps that's what caused your system not to post.
Try installing your boot NVME drive into any slot other than M.2_1, and, if your system posts, then install Windows and update all the firmware/drivers that you need and then replace your boot NVME drive back into M.2_1.
For me, I will either try to flash my BIOS to 2004 (because it has the latest Intel ME firmware rolled up in there) and then to 2103. Or, do what a user on that forum suggests, flash to the latest BIOS 2103, then install NVME in M.2_2/3/4, then install Windows etc. (as shown above). Not sure how stable that will be though.