I’m happy to report that true equality between macOS and Windows is almost upon us now!
No idea what went wrong here, but this should absolutely not be that big. The entire disk is only 1TB large, and I’m not even backing up everything on there. But I guess this explains why Arq kept crashing on my Windows machine all the time. Time to start fresh, maybe it’s because something went wrong when I updated from Arq 5 to Arq 7.