If your computer isn’t within your punching range, SteamVR has a built-in feature for this, called “Knock Knock”. Right click the headset in the SteamVR desktop UI to get to it. It puts a button on your desktop that lets someone click it to alert you in the headset.

The 30% cut was industry standard for digital distribution for years. Google, Apple, and numerous other players all took 30% as standard.

That being said, Steam hasn’t taken a flat 30% for years now - their standard agreement starts at 30%, decreases to 25% after the first $10m in sales, then decreases further to 20% after $50m.

Furthermore, Valve has done more in terms of providing services, APIs/libraries, and end-user features (all with no additional fee to the developers or consumers) than any other game storefront has. I’d say they more than justify their cut.