[ASUS ZenFone 8] b.a.w:
Adding to my posts above from February 18:

I was able to remain on Android 12, retaining the Wi-Fi hotspot functionality, until this morning. I awoke to find a software update notification message, giving two options: update or later. The message also stated that if I pressed later, it would continue with the update in 30 minutes. I rebooted the phone, and the update notification returned, however, lacking the 30 minute warning. A short while later, the phone began to automatically download the update, despite the option in settings disallowing auto-updates being ticked. I force-stopped the system update app, and it stopped downloading the new update. After a short while, it completed the android 13 system update download anyway. I decided to give the 13 update a try again, seeing that there was a smaller update added to the Asus Bios and Firmware download page on March 16th. I proactively backed up my data, knowing that I would likely need to downgrade to 12 again shortly to regain hotspot functionality. I rebooted to apply the base 13 update; no hotspot functionality, as expected. I then downloaded and applied the March 16th (WW-33.0210.0210.269) update OTA; still no hotspot functionality. I plan to downgrade again to Android 12, but I question how long I will be able to use it before another automatic update to 13 is forced upon me by Asus. Does anyone have any advice as to how to activate the hotspot on 13 or a way to guarantee that 12 will not be auto-updated to 13?

Edit: For anyone who might be having the same issue, here is what I have tried and so far, seems to be working. After downgrading to 12, I did not connect to internet during the initial phone setup process. When I did, the phone would already start automatically downloading the 13 update even before the setup process was finished. After setup, I immediately disabled automatic updates both in the regular system settings and in developer options (after enabling these, of course). I find it interesting that before, even with these two settings to disallow automatic updates in use, the automatic update would begin. The only other step I took this time was to disable my system app for system updates per the following method. https://www.xda-developers.com/disable-system-app-bloatware-android/

I understand that this method is likely used more for added bloatware than for system apps, and I questioned at first if it would even work for a system app. Still, after disabling the system update app, it shows "disabled" under its entry in the complete app list in settings, and the system update options in the settings menu are not visible anymore. The main "system" header in the settings menu does show a red dot with "1" indicating that there is something available within the submenu, but as stated there is nothing within pertaining to system updates since disabling the system update app. So far, there have been no other notifications for the 13 update as before. This system update app is easy to reenable, as shown in the link above, so if I want to download the system update later on, it is no problem. I will add to this post if this method fails, but so far, so good.