Questions On Using TWRP And AB Slot Switching

That’s a lot!
I’m not a specialist in that but I’ll try to explain as much as I can.

Device:
-Device only switch slots after installing an update or when you install magisk to the inactive slot or in special conditions like something woes wrong with the update and it changes to the other slot avoiding a brick.
-i guess it doesn’t check data from inactive slot regularly, even when you install a rom or OTA , it just will format the partitions.
-you can always change slots manually, in TWRP or with fastboot command(fastboot –set-active=a, fastboot –set-active=b or fastboot–set-active=other)

Restoring
-when restoring your active slot will be the bootable, if you want to boot the inactive slot(old version of oos or ROM) without installing an update you need to switch slots and flash magisk.
-a boot loop could be a problem caused by many things, you need to find out what was, so in case you ended in boot loop because an update (stock or ROM) you can go back to the previous installed version just switching slots via TWRP or fastboot command(fastboot –set-active=OTHER[this in case you don’t know which slot is active/inactive]) and flash magisk(this will force to boot in that slot)
-if you had a TWRP backup of a working state of your device you can restore it in any slot, only keep in mind that if you want to downgrade, format data is mandatory.

TWRP Flashing

– in a/b devices roms/OTA will be installed to the inactive slot ALWAYS that’s why we can go back to the previous version just switching slots, if you want to flash a rom to the active slot you can do that extracting partitions from payload.bin with a payload dumper(this method is used in android 11 roms right now because of the lack of working TWRP ) and flash one by one partition with fastboot command.
-After flashing a rom you need to reboot to recovery in order to flash magisk, Gapps, kernel, and other mods, because in the moment you flash a rom you are in the active slot but your rom is flashed to the inactive slot, so when you reboot to recovery you let the device switch to the slot where your rom is, so after that reboot you can now flash all your mods.

The next questions about a imaginary switching zip are unnecessary because there’s no zip like that, so no need to worry about that