I’ve done the project conversion and some surface-level testing at GitHub - maxgerhardt/pio-espidf-aws-mqtt-ota: PlatformIO compilable version of https://github.com/espressif/esp-aws-iot/tree/master/examples/ota/ota_mqtt.
The conversion was straightforward as described above except for the embedded files inclusion. The logic had to be moved from CMakeLists.txt to main/CMakeLists.txt with a changed first argument and after the idf_component_register() call to work, as also noted in How to embed binary files into esp32 firmware - #29 by mikemoy. Further the initial compilation didn’t start at all because I somehow had to apply the fix as shown in Use empty ASM and CXX flags if config empty by maxgerhardt · Pull Request #823 · platformio/platform-espressif32 · GitHub.
If you just download the repo and open it in VSCode, it should be compilable + uploadable. Of course, you need to configure it in accordance to the README to get any further.