Restrict combobox value to only items in the dropdown

[chunteck]

Prerequisites

• I have searched for duplicate or closed feature requests
• I have read the contributing guidelines

Proposal

We are using the Combobox inside a Form. We can type any value in the Combobox field, and submit the form. Even if the value does not appear in the list of options for the Combobox, the form can still be submitted. Perhaps we can consider restricting the value for the Combobox to the list of options provided in the dropdown.

Motivation and context

No response