Hi Sjlver, Your post is a great help and got me working. I am adding this to your thread to assist others and save them a bit of time.
I think the Arduino IDE has been updated so your file is now a bit out of date as I had issues compiling FastLed libraries. I found the following after I had manually updated arduino.h:
https://www.electrodragon.com/w/File:Larduino_HSP_v3.6c.zip
Which seems to have all the changes that stopped the compiler. It may still need your manual changes for those who are stuck. I got some compiler errors with automatic type casting. I sorted that by copying the latest platform.txt file from the AVR folder to the Larduino folder overwriting the one supplied in your .zip file.
This website:
https://www.electrodragon.com/w/Logicgreen
Has a significant library of resources including a translated datasheet for the CPU.
To be honest, I think it is a more feature rich processor than the AT Mega 328 and it can run at 32MHz on the internal oscillator. My clones came with 12Mhz crystals but the default is to run on the internal oscillator/2 so you can't tell without forcing the software to use the external oscillator.
You can't program the WAVGAT Nano with a USBASP (I tried) as the 6 pin header does not connect to the correct pins, and if they did I don't think the chip was designed with this in mind.
This link shows how to do it if you don't want to use the bootloader:
https://www.geek-workshop.com/thread-26461-1-1.html
Thanks again for the great post.