The problem is this:
bill85pi:
int blinkPin = PA6;
In the file iotnx4.h is the line:
#define PA6 6
This is the bit of PA6.
The attinycore happens to assign Arduino pin 6 to PA6, however if you had tried this with any of the PORTB pins you would also have found it didn't work with the attinycore. Arduino functions use Arduino pin numbers. To find the correct Arduino pin number to use there is a handy diagram in the ATTinyCore readme(GitHub - SpenceKonde/ATTinyCore: Arduino core for ATtiny 1634, 828, x313, x4, x41, x5, x61, x7 and x8):
So as you can see there are two different Pin Mappings available in ATTinyCore. This can be set in the Tools > Pin Mapping menu. The default one is called Counterclockwise(like ATTinyCore). That's the one you have selected currently. It's the numbers in the diagram marked as "Alternative pinout". That pinout assigns Arduino pin number 4 to PA6. The other option is "Clockwise (like damellis core)". This has the same pinout as the attinycore, which assigns Arduino pin number 6 to PA6, so changing to that selection will make your sketch work but as I said, using PA6 is not right so you need to change to using Arduino pin numbers.