I have successfully used Attiny85 and also Attiny13 with platformio.
It’s essential to have set programmer - I’ve used both an arduinoISP as well as an usbtiny programmer successfully.
Just for your info - it’s possible
Does the hint of ivankravets help you?
If not I could search for my project & configuration.
I managed to upload code now. Thank you for your replies, but there’s still a problem:
If I DON’T add framework = arduino I get this error message:
fatal error: Arduino.h: No such file or directory
since I’m using the Arduino stuff in my program (pinMode,…)
But when I add framework = arduino I get this error message:
Error: This board doesn't support arduino framework!
So what I did was I also added board = gemma since this supports the Arduino framework. I picked Gemma since it also runs an Attiny85, but not sure if this matters and If there’s a better way of doing this.
So this is my working configuriation that allows me to Upload via Programmer: