The boot_app0.bin is something left from really old ESP-IDF versions. Its not required any more. I tested it with recent releases from openmqttgateway by simply not using the additional boot_app0.bin .
The idea behind boot_app0.bin was to be able to switch to boot_app1.bin . Like the partition A and B in Android phones. But it seems like this switch between app0 and app1 was never really implemented in openmqttgateway. The webflasher is still configured to be writing it: Esp32-s3-c1 continually resets - #5 by 1technophile
Am i missing something why boot_app0.bin file is still in use in this project or is this just a leftover that have been forgotten and because it never made any problems using it, it have been kept over the years?