I purchased turbo 2018 and 2019 and i can't download it. What do i do? Can i switch to mac download instead of windows?

There's some contradiction above.   You first said "2018 and 2019", then you said "2017 and 2018."

But in either case, the answer is the same.

Why are you unable to download your purchases?  What happens when you try at this link:

https://shopping.turbotax.intuit.com/app/downloads/

TurboTax Support can provide you Mac downloads in your account if you can't use the Windows version or purchased it by mistake.

You can use this contact form to get a phone number:
https://support.turbotax.intuit.com/contact

In that form, in the product dropdown menu, indicate you are using the CD/download version.

On the next screen, scroll down below the suggested topics (if any) and enter some info to proceed.

They may be open late tonight due to upcoming filing deadline.