I have been searching and am unable to find a proper way to connect the subdomains.
For example, the render domain is example.onrender.com, and I am using Flask and multiple subdomains, my expectation is that I would have `subdomain1.mydomain.com and the other subdomains aswell as landing page.
The free tier gives 2 custom domains and after that you’ll need to upgrade to Pro. You can have your custom domains be subdomains or base domains, and then you configure your DNS provider as a CNAME record to point to your onrender.com domain.
The Render docs have really good documentation and examples for common providers like Cloudflare. https://render.com/docs/custom-domains
So you could do:
subdomain1.mydomain.com→ CNAME to example.onrender.com
subdomain2.mydomain.com→ CNAME to example.onrender.com
But after that you will need to upgrade to Pro to have more than that.