What you want IINA to do:

Support the Apple Human Interface Guidelines on handling animation when the macOS System Preference Reduce motion is enabled.

Proper handling of the Reduce motion preference setting is covered in the Apple Human Interface Guidelines under Appearance Effects and Motion.

The Reduce motion preference was added in iOS after new animations in iOS 7 induced cybersickness in a significant number of people. The preference was added to macOS in Sierra.

In the case of IINA sliding and zooming animations should be suppressed if Reduce motion has been enabled.

What IINA does currently:

IINA currently does not support this preference.

Why you think this should be added:

It is part of the Apple Human Interface Guidelines.

Examples of other projects that have something similar:

This support article for Discord discusses their support for this preference:
Reduced Motion Setting