Is it possible to make nitro cold brew coffee with a siphon? I was wondering, would it be possible to just purchase cold brew coffee, and pressurize it in a siphon with N2O gas? As far as I know, one is supposed to use N2 gas for nitro cold brew, but I wonder how it would taste with N2O instead. Has anyone attempted this before?
I assume that it is possible. However, what will be the benefit? This is my opinion, but... We must try to drink coffee, not generate fancy chemical experiments.

Now, the objective part:

Pressurizing seems quite easy in room temperature. Depressurizing is quite problematic in a siphon. So, it will be a mess when you try to collect your brewed coffee. Or, requires fancy equipment or conditions.

In a siphon, you collect the brewed coffee very rapidly. However, in cold-brew methods, the aim is brewing in a very very long time to extract the floral notes. This, again, seems problematic in your proposal.

The main aim of siphon: you make infusion on top for desired amount of seconds, then, rapidly filter the infused coffee to the bottom layer. If you want to make infused cold brew, the easiest method is still again, going for a french press.