You can setup multiple store views as different subdomains. It’s easy to setup https://devdocs.magento.com/guides/v2.4/config-guide/multi-site/ms_websites.html
Your SEO information should be configurable on a storeview level, you can change scope in the admin for most places - have them to change to the website or storeview and customize it there https://docs.magento.com/user-guide/configuration/scope-change.html