Thank you for the post.
If the field is a "Drop-down list," then uncheck the box "Include arrow to show and hide list" in the Field options section on the Data tab of the Inspector. (See screenshot below). The "Pop-up menu" does not include an option to hide the arrow.
Please note: Report An Issue is intended for Reporting Possible Software bugs. Questions on how to work with FileMaker Pro should be posted in the FM Pro Forum Section. (See tab at top of this screen).