Dropdown field without db column (virtual field only shows first value in list)

Use-case: I have created a doctype and in the form I have use-case where user can perform two operations insert or update on child tables rows.
So I am looking to add new form fields (dropdown and date) in UI where user selects Insert or Update and if update is selected date field should be filled by user and based on selected information I would insert new child rows or update existing child table rows.

Required: Since this dropdown and date field are only used for user-convenience there is no point in storing them in db.

What I tried: I tried virtual field as dropdown field but form shows only first option from the list. I suppose we cannot use virtual field of type Select.

Question: Is there any other way to add custom fields for dropdown and date which don’t have any meaning to be stored in db ? I may have many such use-cases which can increase db columns.
Question2: Is there a way to re-use the fields from Custom Field table (created while customize form) to avoid duplicate entries for same functionality ?

Thanks.

Just learned we can use HTML field for this purpose.