The cancel button in the "Create a Collection.." dialog is disabled by default. In order to enabled it you have enter something or check a checkbox. If you delete the just entered text the button remains enabled.
The Cancel button should always be enabled in order to be able to cancel/close the dialog without having to use the "X" (or on macOS even better the stop light top left).
1Password Version: 8.2.2-23.BETA
Extension Version: Not Provided
OS Version: 12.0 Beta (21A5506j)