Most boards use qio mode. Some ESP8266 modules, including the ESP-12E modules on some (not all) NodeMCU boards, are dual I/O and the firmware will only boot when flashed with --flash_mode dio. Most ESP32 modules are also dual I/O.
In qio mode, two additional GPIOs (9 and 10) are used for SPI flash communications. If flash mode is set to dio then these pins are available for other purposes.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Hmm, so first try qio and if it does not work try dio
Found this hint on https://github.com/espressif/esptool#flash-mode---flash_mode--fm
Which ESP board is on your Wemos board?