How to delete GameCenter and iCloud from Internet Accounts using the Terminal?
The Internet accounts are stored in ~/Library/Accounts/Accounts4.sqlite.

give your terminal full disk access or you can't access ~/Library/Accounts
create a backup (e.g. cp ~/Library/Accounts ~/Library/Accounts.bak
open it with sqlite3 or any other sqlite client such as DB Browser for SQLite
give full disk access to your sqlite client (important if using a client with a GUI or its own wrapper, such as the above)
SELECT * from ZACCOUNT;
delete the row you want gone
save
reopen Internet Settings

This helped me get rid of a broken Game Center account on Big Sur. The account caused the Internet Accounts dialog to freeze.
credits: https://www.telnetport25.com/2020/04/macos-catalina-there-was-an-error-in-internet-accounts-preferences/