If anyone else ends up here like I did.
To drive the DIM Control pin without pulling from Vdd, try this.
This will keep the micro isolated. This assumes that you use a dual optoisolator, and that the CTR is the same. To ensure they ARE equally matched, you can buy the more expensive IL300 or LOC110 - built especially for this purpose.
Also do note: if you are going to make a DUAL dimmer, then do NOT connect the 'GND' between dimmer A and dimmer B. They must be separate.
@skywatch do Fluke meters work unattended in enclosed cabinets or walls, using varistors for power supply 24/7?
As I've said I prefer using a better power supplies with built-in over-voltage protection. As for how it is achieved without a varistor you can find plenty information by yourself using google.
@NeverDie i can speak for arduino side im not sure how it works for CircuitPython. virtual hard drive part is only true if there was a bootloader prior to update. im not sure how nordic ships their dongles but i think they dont install adafruit bootloader inside of them so you need a fresh bootloader install and it is easy but you need jlink for that. after connecting your jlink to nrf52 open the arduino from menu find jlink for adafruit nrf52 and then just simply click install bootloader and voila it works with arduino.
but then again that usb dongle wont work seamlessly with adafruit bootloader because im sure adafruit has different pin maps you just need to check their pins from variants file and match them on paper to the dongle so when you write your code you know which ones to use, unless theres a seperate variants file specifically made for this dongle.