Suddenly closing your source doesn’t magically fix all existing security issues in your code which have not been identified yet. But it sure will prevent the community from helping to fix it.
Besides that, it is also a dick move to everybody who helped grow your product. Why would I now, or ever do anything with/for cal.com after this action. Why would I do anything for their hobbyist “fork” cal.dyi . They just threw away all the trust they created.