Android - When installing new ROM through fastboot, which .img files must be flashed, with what arguments, and in what order?

I own a OnePlus 7 and the same developer has answered a similar question in One Plus 7 device forums

Question

I just noticed, the script in bat file only flashes 25 .img files, but when I extracted payload.bin in OB2 I saw 32 .img files. Does this mean that the other .img files in payload are not needed? Or can I add the command in bat file to flash other images?

Answer

They can't be flashed using fastboot, that are the criticals partitions, they are needed and it's for that these fastboot roms can't be used to update or downgrade the software you have on your device, because the fastboot roms can't flash all partitions. This fastboot roms should be used if your system cannot be used and if you don't have access to TWRP

• They need to be flashed in the order specified. All of them (see next point)

• .img files replace the file on the device with the one in fastboot ROM, except for critical partitions (I am not sure what these are for your device but could be boot loader, OTA, TEE, SoC etc) . This accounts for the difference in number (31 extracted but 19 only flashed). See Irfan's comment

• --disable-verity is only applicable for vbmeta header files. For more details, see How to disable dm-verity on Android with "user" build type ROM? where the concept is well explained, in detail.