[OnePlus 9 Pro] Zhono:
Managed to update, this time without having to factory reset my Galaxy watch, or having to clear my Galaxy Buds+ settings and pair those again..

Steps are simple enough, if long.

Enter recovery, and check your active slot. You MUST end up on the same slot after all is said and done. So for me slot A

Reboot to bootloader and flash the new bootloader to BOTH slots. I specify 'boot_a' and 'boot_b" in the flash command, just to be sure.

Back to recovery, sideload the update. It will flash to the inactive slot. For me slot B.

Do NOT reboot yet. Turn OFF your watch, or it will attempt to connect to your phone and Samsung's app will get angry. Only after turning off your watch, NOW you can reboot. You phone will now have swapped the active and inactive slots. So for me, slot B is now active.

Give it a few seconds to load up and do what it's going to do, then reboot back to recovery. The active slot should still be whichever slot was NOT active when you started. Again, for me, slot B.

Sideload the update again. This time it will flash to the slot that was active when you first started, For me slot A.

After the update, reboot directly back to recovery, and check the active slot again. You should be back on the same slot that was active when you started. Again, for me, slot A. If you are not(you really should be, but we're just triple checking), reboot to bootloader, and set the active slot to the correct one with the command 'fastboot --setactive=a' or 'fastboot --setactive=b'. Whichever one you need.

You should now reboot your phone and let it boot up and fully load. If you are NOT rooted, you should be done. Turn on your watch and it should be able to connect just fine without factory resetting it.

If you WERE rooted, don't turn on your watch quite yet (shouldn't actually matter, but again, we're just being extra careful). Instead, reboot back to recovery yet again. Sideload your Magisk zip. It will flash to the currently active slot. It will NOT automatically swap the active and inactive slots.

So reboot to bootloader and swap to the inactive slot yourself with the commands from step 7.

Back to recovery. Sideload the Magisk zip again. Magisk is now flashed to both slots.

One more time, reboot to bootloader and set the active slot to the one you started with at the beginning. Again, for me, I started at A.

One last time, reboot back to recovery and check the active slot, just to be sure. Again, you should be on the same slot you were on before you started this whole procedure. If you are, reboot the phone and you should be good to go. Turn your watch back on and it should connect. You might have to open the Samsung devices app and hit the button to connect the first time, but it should just work, and not complain to you about needing to factory reset the watch to pair.

My instructions were long, and probably overkill, but doing all of this only really takes a few minutes. And I HATE having to factory reset the stupid watch after every rom update. For anyone wondering why I bother to do all of this instead of just flashing the update once, flashing Magisk to that same slot, and calling it a day; it's because sometimes the phone likes to crash, then force me onto the other slot. It's nice to have everything working properly on that slot as well, including root. Though to be fair, my phone used to crash a LOT on the February update, but after the March update came out, it hasn't crashed even a single time. Let's hope this update is just as good.

Oh, and yes, I have tried "easier" methods, like using the partition copy script, or manually backing up the bluetooth partitions and restoring them, etc. Didn't work, my bluetooth connection were still borked after updates through the Derp updater in the rom.