The native speed menu is available in apps that use Apple's video player. The feature isn't mandatory for developers, so it might not be available in some apps.
Developers are able to modify Apple's default speed options, but they are only able to change them to 1.0, 1.0, 1.25, 1.5, and 2.0.
The speed menu can be reached with the tap of the icon with three dots around a circle. You can find the menu in supported Mac apps by selecting Playback Speed. There is a new timer icon in supported Apple TV apps.
With no changes required, Apple says all apps with the new iOS, iPadOS, macOS, and tvOS SDKs will have this feature. Developers who want to completely remove the menu can use the new APIs added to AV Player, with more information available in the session video.
Some Apple apps, like the Developer app, use a custom video player to control the speed at which the video is played.