Can you actually turn a garage into a decent remote work space?

Yes, but you've got to do it smart. The main thing is decent soundproofing (a regular door won't cut it) and good lighting, because working in a dark garage will mess up your eyesight by day three. Ventilation is also critical if you're spending 8 hours stuck in there, so consider getting an extractor fan or leaving a window open. The rest (desk, chair, extra outlets) is the easy part; the hard part is convincing your brain that it's a real workspace and not some cave you're hiding away in.