I prefer not to have spy and bloatware on my computer.

1) How do I make another user account for steam?

2) Will putting it in another user account isolate it from my main account so it cannot sell my data for money?

If they would put more moder linux games on gog, like the Metro series, this would not even be necessary.

Aren't you a little bit too paranoid?

If your that worried about steam, why are you using it in the first place? Anyways, all internet based systems extract data all the time, this one, your email, even your OS to varying degrees, just unplug the net that's the easiest way.

As for your question, another user account will still have access to the same drive (unless you set it up differently), so I don't how that would help, although it wouldn't be able to see the user specific Documents and such like folders.

There are bigger problems than Steam.

Like nc intimated, if you are worried about Steam you'd better get rid of your email account, Windows, whatever AV you are using, Facebook (if you use it), and now that I think about it, better stop using the internet all together.

Didn't actually see MINT in the title. Anyways, not sure if something like this:
https://www.sandboxie.com/

Exists for MINT.

Funnily enough, we ended up talking about sandboxing utilities for Linux in one of the other 2,000 threads the OP has created the last few days.

Were you planning to log out and back in as a dedicated gaming user every time you want to game? If so, creating such a dedicated user is really simple, check your distributions documentation for details. Assuming sane file permissions, this will help a bit against potential intrusions: it won't be trivial for steam to list or read the files on your regular account, for instance. But while it's running it can probably still for instance take screenshots (may not be a big deal if all you do is game while it's running) or listen to a microphone. Probably some other stuff too that I can't think of right now.

It's fairly pointless to go to such lengths yet install steam as root using the provided *.deb package. There's probably instructions somewhere on how to do it with user permissions, but it will get complicated.

It's also possible to run steam as another user while being simultaneously logged on to your normal account, but you'll lose some of the benefits. It may still be kept from reading your files, but to do anything useful it will still need permissions to your screen and audio device. This time you may be have your email or banking open while running it, so it gets possible to take some fairly intrusive screenshots, or to covertly listen to you when you forget that its running. I don't think it's likely that it's doing any of these things, but it sure could, easily.

I saw instructions for the last bit somewhere not long ago, but can't seem to find them now.

Maybe ditch Mint for Qubes OS?

I'm not sure how well games work in Qubes, but in terms of sandboxing things, it doesn't get much better.

As much as I dislike steam, I have never known Valve/Steam to sell accounts.
However if someone hacks your account the hacker will probably sell it.

Unfortunately, Qubes OS isn't suitable for games that require 3D acceleration.

From https://www.qubes-os.org/faq/

Can they still delete all your data?!

I run all of my Steam games in offline mode. As far as I know, that don't have any of my save data; it's all on my PC.

Now being in offline mode means no achievements but I could give a fart about that.

(Assuming the program you're running does not take advantage of a security vulnerability):

A program can access and delete all files owned by the user the program is running as. This means that, if you run a game as the same user you use for your work, the game can access and delete your work files, but if you run the game as a separate user, the game is not able to do so. Said game, however, still has full Internet access (assuming the computer has Internet access), and can still access the save data of any other game being run under the same user account.

Incidentally, SteamOS actually has two main user accounts: One for Steam (which can't use sudo to get root access), and one for the desktop environment (which does have access to sudo if you need root). Hence, even SteamOS separates gaming from other tasks with a separate user account, so it is likely good practice to do so.

(There might be issues with a game recording video/audio from a desktop session, of course.)

Look at this shit! So now, I gotta pay $5 just to talk about how crappy steam is?

"Having trouble accessing a Steam Community Feature?
New accounts are limited from using all of Steam's community features. You'll have access to all of Steam's features once you've spent $5.00 USD in the Steam store or added $5.00 USD to your Steam Wallet. Some of the features that you won't be able to access are:

Adding friends on Steam
Buying or Selling items on the Steam Community Market
Creating a Group on Steam Community
Creating user reviews or rating artwork, screenshots, workshop content, or Greenlight submissions
Using Friends chat in your Browser or on a Mobile device"