[werk_ag]

I think the issue is I'm using a Mac which in last few OS versions dropped all 32bit support.
I will re-try on a Windows machine, which still supports 32 and 64 bit at the same time.

... as after searching on the internet all suggestions were to use a later AVR version.

Those suggestions while valid and recommended when starting a new project, not always apply for already existing projects, as many may use customized libraries that may work well with latest AVR boards version.