On the English Wikipedia, I only have five user sandboxes:

User:3PPYB6/sandbox, for making test edits that probably won’t get published.

User:3PPYB6/sandbox2, for a list of my total Wikipedias. An alternative to this would be my global account information.

User:3PPYB6/sandbox3, just showing the main page. May someday include me vandalizing my own sandbox, but that is contrary to Wikipedia.

User:3PPYB6/sandbox4, for hosting my April Fools' user page! Just wait till 2023…

User:3PPYB6/sandbox5, used for testing MediaWiki messages in case…

If I create a new user sandbox, it will show up on here.