Playing off a USB Stick?

Yes, my problem deserves some amount of mockery, but genuine advice would also be appreciated.

I've got BG3 on Steam, and was playing it on my flatmate's PC for a while, but that's since stopped working. The only computer I own myself is a MacBook Pro 2020, which (shockingly) should still be able to run BG3.

The only issue is my storage space. 144gb might not be much to someone with a 2TB drive, but considering that I've only got 20gb left on my 500gb drive (which also has basically everything else I need on it), I've been thinking about creative alternatives.

If I buy a 256gb USB-C stick, and install Baldur's Gate 3 onto that, am I going to have terrible, crazy bugs and issues? Will it be absurdly slow? Has anyone else tried this?

Any advice would be greatly appreciated!