HTTP/1.1 is no different from HTTP/2 and even HTTP/3 when it comes to multiple domains. The optimization strategies are all aimed at solving simultaneous resource requests from a single host (not domain but close enough) - should be obvious when you consider that each host requires at least one separate socket connection anyway.
In practice http/1.1 with 1 connection per request even encouraged making more domains/subdomains if you wanted to have more simultaneous requests
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HTTP/1.1 is no different from HTTP/2 and even HTTP/3 when it comes to multiple domains. The optimization strategies are all aimed at solving simultaneous resource requests from a single host (not domain but close enough) - should be obvious when you consider that each host requires at least one separate socket connection anyway.
In practice http/1.1 with 1 connection per request even encouraged making more domains/subdomains if you wanted to have more simultaneous requests