I think you mean LiveUSB, but it depends on the game. If it's a large game, it's going to install and run from USB, so it's not going to perform well. Small games that fit in memory will be fine.

If you want to specifically take steps to make this work better, get an external SSD and turn the Live Image that way. It's still not going to perform well with large games, but multitudes better than from USB.

Unless you have a specific game to try, you'd get better info from ProtonDB, or comments online to find out what the general feeling about performance is going to be.

Performance will likely be really bad running on a live ISO since you are going to likely be bottlenecked by read/write speeds of the usb you have plugged in. I wouldn’t use it to test performance of games.

Yes, though depending on the media you are running the OS and game from, the performance could be worse than you would expect from an install on the main system media. For example, when I was testing moving over, I had Arch installed on a USB device and had some issues with I/O bandwidth. But, I also had a folder on my main storage drive to run Steam games from and this performed OK. It was formatted NTFS; so, there were some other oddities. But, it worked just fine and managed to convince me that I'd do OK under Linux. Took the plunge and I've been happy with the decision ever since.

Yes but it will depend on your RAM (If liveusb copies it to ram) or USB

In a live environment I was not able too install too much - it always ran out of space, but I am not even sure what space it used, maybe a RAM disk?

So if Steam even fits with all of it's dependencies, you may be able to try out a tiny game, definitely not 150GB Forza Horizon 5.

There are ways to make it work by using persistent storage, but it's a hassle, at this point it would be easier to buy a 25$ 500GB ssd and install Linux on it.

try it