The January 2020 patent, “USING AN ALTERNATE INPUT DEVICE AS A MANEUVERABLE EMULATED TOUCH SCREEN DEVICE” suggests the simple solution of entering a mode where your trackpad pretends to be a touch screen, delivering touch inputs to apps as if you are touching the screen instead of trying to control the cursor.
Microsoft notes however that a trackpad is generally a lot smaller than the screen, and their solution is a movable input area (the lighter box in the drawing above) which can be positioned via a two-finger swipe, which would then move the input area where you want to the desired touch input to take place (e.g in the example drawing a signature with your finger).
As mentioned earlier, while the solution would be pretty awkward to emulate a whole touch screen, it may work pretty well for the much smaller windows of phone apps being streamed to your PC.
The full patent can be seen here.
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