GoG Galaxy keeps trying to download a new update for SS2 but fails (possibly because I have mods installed).

Is there a new patch being released or something (its 195 mb in size)?

yes, a small update should be going live soon, definitely not 195mb though - Galaxy is most likely trying to "repair" your modded install. that's why we recommend keeping a modded install separate/out of galaxy/steam.

you may have to repatch with the tool and reactivate mods should the client succeed in updating your install.

I see, thanks.

Can you not turn automatic updates off for that game? Not a Galaxy user here but that seems like how it should work.

right, Galaxy, unlike steam, will actually allow you to turn automatic updates off - I'd recommend doing that if you are running modded and/or keeping the game up to date using SS2tool.