Today Apple released a warning to iOS 13 and iPadOS users about a security issue affecting third-party keyboards.
Third-party keyboards can run standalone with no access to external services or can request "full access" to provide additional, more enhanced features. A bug in iOS 13 and iPadOS can cause keyboard extensions to be granted full access even if full access hasn't been approved.
Apple stated that the bug does not affect Apple's built-in keyboards, nor does it have any effect on keyboards that don't actually use of full access of the system.
Until a fix is released, iOS users concerned about their data and the access granted to third-party keyboards are advised to temporarily uninstall third-party keyboards.