ESP32 web installer -> invalid header: 0xffffffff

[glowingkitty]

Hey there,
I tried to fix my web installer for my open source LED controlling software, after noticing that your web installer also works on the eps32 s3 (which I didn't manage to do earlier). Now I updated my web installer with some learnings of your web installer and the flashing works, sort of. But now the USB serial outputs only:
invalid header: 0xffffffff in an infinite loop.
Any idea how to address this?

manifest.json:

{
  "name": "Project",
  "version": "0.15.1",
  "home_assistant_domain": "leds",
  "builds": [
    {
      "chipFamily": "ESP32-S3",
      "parts": [
        { "path": "../bootloader/esp32_s3_bootloader.bin", "offset": 4096  },
        { "path": "../firmware/project/partitions.bin", "offset": 32768 },
        { "path": "../firmware/project/firmware.bin", "offset": 65536 },
        { "path": "../firmware/project/spiffs.bin", "offset": 3342336 }
      ]
    }
  ]
}

Working platformio config:

[env:project]
board = esp32-s3-devkitc-1
platform = [email protected]
platform_packages =
upload_speed = 921600
build_unflags = ${common.build_unflags}
build_flags =  ${common.build_flags} ${esp32s3.build_flags}
  -D CONFIG_LITTLEFS_FOR_IDF_3_2 -D WLED_WATCHDOG_TIMEOUT=0
  ; -D ARDUINO_USB_CDC_ON_BOOT=0 -D ARDUINO_USB_MSC_ON_BOOT=0 -D ARDUINO_DFU_ON_BOOT=0 -D ARDUINO_USB_MODE=1 ;; for boards with serial-to-USB chip
  -D ARDUINO_USB_CDC_ON_BOOT=1 -D ARDUINO_USB_MSC_ON_BOOT=0 -D ARDUINO_DFU_ON_BOOT=0 ; -D ARDUINO_USB_MODE=0 ;; for boards with USB-OTG connector only (USBCDC or "TinyUSB")
lib_deps = ${esp32s3.lib_deps}
board_build.partitions = tools/WLED_ESP32_8MB.csv
board_build.f_flash = 80000000L
board_build.flash_mode = qio

and the partitions.csv:

# Name,   Type, SubType, Offset,  Size, Flags
nvs,      data, nvs,     0x9000,  0x5000,
otadata,  data, ota,     0xe000,  0x2000,
app0,     app,  ota_0,   0x10000, 0x200000,
app1,     app,  ota_1,   0x210000,0x200000,
spiffs,   data, spiffs,  0x410000,0x3F0000,

[rbergen]

I'm converting this to an Q&A discussion, because it does not concern an issue on NightDriverStrip.