Have you tried small mode? It's a built-in option.
https://www.howtogeek.com/694531/how-to-reduce-steams-ram-usage-from-400-mb-to-60-mb/
https://www.xbitlabs.com/blog/mini-steam/
(The instructions are Windows-centric, but the process is pretty much the same on Linux I think. You can figure it out)