set board_build.flash_mode to fix missing sdkconfig.h

platformio.ini

@@ -440,6 +440,7 @@ lib_deps = ${esp32_idf_V4.lib_deps}
   ${esp32.AR_lib_deps}
 monitor_filters = esp32_exception_decoder
 board_build.partitions = ${esp32.default_partitions}
+board_build.flash_mode = qio ;; TODO: is this the correct flash mode?
 
 [env:esp32dev_8M]
 board = esp32dev