[OnePlus 8 Guides, News, & Discussion] sbpetrack:
Thank you so much for this reply... I was too busy actually USING my phone to reply quickly. A few questions please. I can't tell you if these are OnePlus 8 specific, but I'm pretty sure that some are and some aren't:

1. First, most important: I installed the Magisk-patched boot.img only to slot a. Is it my job to ALSO install it to the other inactive slot, or should/must I not do that?

2. While on that subject, I understand how the A/B scheme improves the update process, but can I use it to help me when my phone borks outside of the update process? That is, if my phone crashes/freezes/whatever, but I can still fastboot, is it possible that I can just switch the active slot with fastboot, and reboot, and be happy? (Of course I understand that you can't "guarantee" that this will work, obviously. My question is if it is a viable thing to try.) And if it does work, is there a fastboot or other command which would then just "copy slot A into slot B"? I've often wondered if between this A/B scheme for the OS and a journaled files system for userdata, why my phone should EVER freeze and require a wipe. For example, right now, if I made the other slot on my phone active, would i just go back to IN21AA, so that I could update to Global without a wipe?

3. Is it possible that my IN21AA phone itself downloaded and installed an OTA update which made it into an IN21DA phone?

I am really pretty sure of the following two things (although I am even more sure that, as the musical "The Short Reign of Pippin IV" sings: "the only thing to be sure of, Mate, is there's nothing to be sure of"):

a. I used Magisk to uninstall Magisk=> restore images. And then chose to download & install the OTA update from the "System". And because I had read in the Magisk docs that there is no longer the possibility to "install Magisk to inactive slot", I just clicked on the "Reboot" immediately after the OTA update. I knew that this would lose me root and Magisk, but I didn't care: I just patched and installed boot.img, reinstalling Magisk again from scratch. This appeared to go fine, though afterwards neither Wifi not telephone calling worked. Although my phone was rooted.

b. It was then ( I think) that I looked and saw the full OTA .zip on my phone. I can only assume that this .zip was "the" OTA that my system had just used to update. It is true that I had been looking for the 11.0.7.7 .zip for some time before all this -- I had been hoping to avoid the actual OTA process and just sideload the update, since I knew that in any case I was going to have to manually patch boot.img anyway. I rather assumed that the huge 2-3GB .zip would not remain on my phone after the update. so...

After an OTA update, does the .zip file usually remain on the phone, or is it removed at the end of the update process? (Of course, since "something" went wrong, this still won't tell me if the fact that it was on my phone was the result of the update, or the result of the fact that I actually found the .zip file at some point earlier and downloaded it, but didn't realize it. After all, when I was looking for it, my phone was rooted, so perhaps I downloaded it to somewhere but didn't realize it, who knows?)

4. Since my phone now says "IN21DA", does that mean that all future OTA updates will -- under normal circumstances -- only be to IN21DA? The fact is that I'm not in India, I'm in Israel, and my phone knows that. If everything 'seems' to be working, can i just wait until the next upgrade and get IN21AA back?

5. If everything seems to be working, should I worry that there might be some "invisible" problem? If my phone starts data-roaming even though it's at home, I'll see the "R" in the indicator at the top. I want to take seriously your advice to return to Global, but not only would I prefer not to wipe (again) -- I also generally also take seriously the principle that "if it ain't broke don't fix it".

Thank you for any/all advice/answers/explanations!