In total there are 4 Demo versions on MS-DOS: 8-bit, 24-bit, 3Dfx and 3Dfx Special. Here are 3Dfx-Demo and Special 3Dfx-Demo for MS-DOS.
In general, there are few differences from the full version. Well, except for having only one city (Liberty City) and having a timer at the top of the screen when you're playing. It ticks, and it ticks hard. When you start a level, the timer starts counting down, after 6 minutes the game process ends. But don't worry, 6 minutes won't run out forever. You can always restart the game. When you restart the game, the timer will start moving again and count down 6 minutes.
Both demos are difficult to run. When trying to run on modern systems, an error occurs related to the Glide drivers. Normal launch is definitely possible with a real Woodoo 3Dfx card on MS-DOS and Windows95/98. But somehow it can be run on modern systems. If you somehow succeeded, then write in the comments what helped you. If it works, then we will indicate your launch method here.