Could somebody help me change where Steam installs Proton/compatibility stuff to?

I'm on Mint. I have two partitions, one at 100GB I set up for the main OS installation, and another 1.9TB installation I use for storage. But the first partition is getting some storage issues, which comes partly from Timeshift (which I already redirected) and partially from Steam, specifically Proton. I want to redirect Steam onto the larger partition, but the space Steam takes up in this way is taken up by several smaller files and folders that add up to a lot, so I feel unsure about how to change things properly.

And a follow-up question, is it safe for me to expand that smaller drive with Gparted or something, or would that put the data on it at risk? Since it's the OS partition, that's important data.