Seems that both options for Variable Refresh Rate and Allow Tearing are coming to the Steam Deck in a future update (thanks Reddit), here's what that means.
Firstly, no, the Steam Deck itself will not have VRR, as the screen doesn't support it (As confirmed by Valve developer Pierre-Loup Griffais on Twitter). This will be for external screens when docking. The point of VRR is to have your screen continue to dynamically change the refresh rate to match the game, enabling it to remain smooth and tear-free.
As for the Allow Tearing option, this is due to the current way that Steam Deck Gaming Mode works with the Wayland display server, with it always forcing VSync. Once ready, this will allow you to properly have it off, and therefore reduce any extra latency it introduces and get some tearing.
Both of these are going to be pretty big and exciting additions, especially for those with VRR capable screens and for times where you really need that little bit extra input performance.
The options turned up in the Steam Deck "Main" updates channel, which is one of the extra update channels you can turn on via Developer Mode not actually meant for users. As with any in-progress developments, it can change at any point.