What to do with a thesis adviser that doesn't respond to emails or offer any help?
You are a bit stuck. It would be a shame to abandon work already done if it shows promise of successful completion. 

But there are really two things that you should require from your advisor. First, they need to approve of your thesis when complete. Second they need to write you a good letter of recommendation for the next stage of your career. 

Everything else is nice, but not essential. If you are capable of doing the work on your own and can achieve those two things, nothing else will matter. 

I'm more concerned, actually, that no one responds to your request for help. Perhaps if you take a different approach with external professionals it would be more successful. My preference would be short introductions and very simple explanations about what you are working on. Make it easy for anyone to make the first response. If you send too much it is more likely to get ignored. 

Quit and restart elsewhere only if no other option is open to you. Given the current pandemic (early 2020) no one will think poorly of you if you need to start over. It will delay your career, but not necessarily end it.