I brought a domain (not in AWS) and parked it on AWS. I also got a certificate in AWS Certificate manager, for a domain I use for a shopify store. On the shopify admin, I see that SSL isn't available for the purchased domain.
Is there a way to connect the domain with the certificate if the server is actually on shopify ?
ACM certificates are only for use with CloudFront and Elastic Load Balancers. You could possibly setup a CloudFront distribution in front of your Shopify domain in order to use the certificate that way, but it's probably more trouble and expense than it is worth.
You might look at moving your DNS hosting to CloudFlare and using their free SSL service.