Can I run gpt2 on a Mac with 64 GB?

Yes

Its published weights (548 MB) fit in the 48.0 GB a Mac with 64 GB can use, with room for ≈ 1K tokens of context.

hf download openai-community/gpt2

Files and context on Mac with 64 GB

Each file of gpt2 (and of GGUF versions the site has analyzed), and how much context fits next to it, with the context cache in 16-bit or 8-bit.

gpt2 on other hardware

Popular models that run on Mac with 64 GB

Assumes 75% of the Mac's memory is usable (macOS's default limit for the GPU; it can be raised) and at least 4K tokens of context for one conversation, with the context cache in 16-bit unless noted. Fits leaves at least 20% of that memory for context; Tight leaves less.