Hello @dominique,
You have likely seen this pinout from the datasheet:
I don’t know if this will work as described as initial start-up current may be a problem. While the Q015-5 is rated for 100 mA (no load) and 250 mA (full load), there may be higher current as it turns on.
Know that the 5 VDC rail on an Arduino R4 WiF is derived from the VBUS of the USB connection (see schematic). Consequently, the Arduino’s power supply could also be an issue.
Recommend isolating the DC-HVDC converter from the Arduino. Use a bench type power supply if possible. Once it is working you can revisit the Arduino.
Sincerely,
Aaron