Digispark uploading not working in KDE Neon (Linux)
I had the same problem when using the snap package of the Arduino IDE. I solved the problem by installing the Arduino IDE from the official web page: https://www.arduino.cc/en/software
You might have to run the Arduino IDE with sudo or better add a custom udev rule in case you now get following assertion error:

'micronucleus_connect: Assertion `res &gt;= 4' failed.'

Solving the assertion error is further described in following post: https://digistump.com/board/index.php?topic=106.0