Audio/video buttons shown on MacOS 11.7.10 despite CallKit support only in 13.0+

[germanicianus]

Describe the bug
According to below page, CallKit support is available since MacOS 13.
https://developer.apple.com/documentation/callkit/
When using Siskin IM on a MacBook M1 with MacOS 11 (Siskin IM normally installed from AppStore), the audio/video buttons are shown despite the functionality won't work. Using them results in different behavior depending on the contact's client.

To Reproduce
Steps to reproduce the behavior:

1. Within Siskin IM on Mac, initiate a video call with a contact supporting that.
2. When the contact uses Siskin IM also, a message that the call failed is shown. For Dino, it's forever connecting.

Expected behavior
The audio/video buttons are either not shown or disabled with a hint that this functionality is only supported on MacOS 13+.

Screenshots
Provided if needed.

Details (please complete the following information):

• Siskin Version: 7.3.3 (4)
• iOS MacOS version: 11.7.10
• iPhone Mac model: MacBook Pro M1

Additional context