While I realise this may be a result of intentionally making the menu reflect the user experience where the stream camera takes over the VRChat window render.

But when using Spout, it should not be forced off, as I've been using this feature since the day Spout became available to stream in a dual perspective with stabilisation on both at the same time without issues.

(Video to show how it forces the steadycam off when Spout gets enabled, and screenshots to show how it used to work and let me have 2 perspectives at once for content flexibility)