Would be great to have a simple and nice API for creating custom post effects with the new CameraFrame system.

Currently, docs: https://developer.playcanvas.com/user-manual/graphics/posteffects/
As well as the engine: https://github.com/playcanvas/engine/tree/main/scripts/posteffects
Contains old post-effects, while they all are deprecated. And does not work out of the box when used with recent engine (requires to use class instead of prototype inheritance).
Also, the old system does not mix with the new system, if you try to use both systems together, it simply renders black screen.

It would be great to have a proper new system, that allows an easy way to define custom post-effects, and add them into the queue in CameraFrame.

New system while it has higher quality effects, it really lacking in examples and flexibility for custom effects.
It is not even possible to override its implementation chunks: #7921