That's unfortunate. Sounds like your computer probably doesn't have enough RAM to properly play the game. The only reason it was likely working on Windows was because Windows will work, albeit very slowly, with max RAM usage, whereas Linux has tools in place (as you discovered) to avoid that, since the system will freeze of RAM usage maxes out.
Sadly there isn't really a good solution to this I can recommend besides buying and installing more RAM, which with current prices isn't the most feasible option. Not to mention it involves opening the computer itself which I have no idea how comfortable you would be doing that.
There are a few things you can do software side to try and maybe make it work, but none of it is simple and it's not guaranteed to work either. This is an issue that swapping distros could help (though it may not outright fix it) as you can install something more lightweight that uses less memory. You would likely also want to change desktop environments as KDE Plasma does consume a fair bit of memory. That being said, I have no idea how easy it is to get Steam up and running on distros designed to be lightweight, so it may involve some additional downloads that defeat the entire purpose of it being lightweight.
Another option on the software side, would be to set up a swap partition. It uses the internal storage drive as a sort of backup memory. It's not guaranteed to fix your issue either, as it comes with some limitations. I don't have experience setting up a swap partition on an already installed drive, so I wouldn't be able to walk you through it. It would probably be easier to reinstall the OS and make sure you create a swap partition at install.
If you do decide to change distros to try and free up some more system memory, some lightweight alternatives I could suggest, based on what you're currently using, are Lubuntu, or Linux Mint using XFCE or MATE. Again, I'm not sure how easy it would be to setup Steam on a lightweight distro so it's up to you if you even want to try changing distros.
Looks like I may have spoken too soon about the RAM.
I decided to double check your actual laptop specs with a quick google search, and it looks like it uses DDR3L-SDRAM (I would suggest double-checking and confirming this yourself). If that's true, since it's an older type of RAM it hasn't actually been hit by the RAMpocalypse much at all and it's actually pretty cheap. I would recommend 16GB minimum for most modern gaming but make sure your laptop supports however much you decide to install.