Missing radio to enable default signature on iOS 17. device

Summary

There is a radio field missing that allows a user to enable a signature on an iPhone (responice UI) with a specific version of iOS. Hideo and I we can both reproduce it an on an iPhone 15 (iOS 17.5 - xCode simulator or Chrome simulator). The option "no signatue" is selected by default and there is no way to enable a default signature.

On an iPhone 14 however (iOS 16.6 - Chrome developer mode) you can enable the signature.

Basic Information

• Affected versions: 7.10.x
• Environment: On-Prem
• Reproducibility: always
• Customer: IIJ
• OTRS Ticket Link: https://otrs.open-xchange.com/otrs/index.pl?Action=AgentTicketZoom&TicketNumber=2024051410000124

Steps to Reproduce

1. Use any iPhone device or simulator with a recent version of iOS
2. Login to AS and change to Settings → Mail → Signature
3. Try to enable a signature

Expected Behavior

Only on radio

Actual Behavior

A radio field is shown in front of the textarea, so you can enable a default signature.

Screenshots

iPhone 15 on iOS 17.5 - as expected

iPhone 14 on iOS 16.6 - radio in front of the text field

Misc

As a side effect, it actually shows "false" as signature when using my account. I assume the responsive web UI comes with an individual signature, as my usual default one is not shown.