If you go to a game on Steam, find the gear icon, go to Manage and select Browse Local Files...

For most Unity games you will find a file called "UnityCrashHandler..." executable right in the folder that opens.

Not easily, but if you become a game developer you can start to tell at a glance. Unity games have a very specific type of jank and look + feel. (So do Unreal, Source, and Godot games.)

Even if a game is highly stylized, a Unity game always "feels" like a Unity game. Kerbal Space Program, Pokemon Brilliant Diamond/Shining Pearl, Pokemon Go, Cuphead, Untitled Goose Game, Cities Skylines, Valheim, etc. It's a combination of physics, shaders, and input latency that's hard to put into words.

The closest I've come to seeing a game that breaks out of the "made in Unity" feel is Stanley Parable Ultra Deluxe, which was made in Unity but pretends to be made in Source (the original Stanley Parable was made in Source).

~~Forgive me if I'm mistaken, but last I know of, any games made with Unity start up with their name and logo first, or at least shortly after their intro.~~

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