You can host and serve it from the origin server, why not?
No need to go for a solution with Cloudflare then.
Furthermore, if your domain is using Cloudflare, simply you could return a JSON using a Worker on an route (path) e.g. example.com/.well-known/assetlinks.json.
Example:
To make it work, make sure your DNS records for your hostname such as example.com and/or www are proxied and set to under the DNS tab of Cloudflare dashboard for your zone.
Make sure to bound your Worker to the example.com/.well-known/assetlinks.json.