AKAIK, there is no hard-coded code limit in Magento 2 to create the website, store, and store-views on a single instance by leveraging the multisite concept.
You can create as much as you want, but there are so many scope level limitations (Few components have a global scope) when you are working with the multisite concept.
Also if you create this many site, store, and store-views, the performance of the site will not be the same and it will definitely impact the overall performance as the complete build gets bulky so.
Performance is something that also depends on the server and its configurations/capabilities, so look to evaluate that as well.
Hope it helps !
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