each Steam game you have which uses Steam Cloud saves has a specific quota for storage, this quota varies quite a bit, but some games have quite a lot of quota:

• BeamNG.drive: 953.67 MiB
• Disco Elysium: 93.13 GiB
• Euro Truck Simulator 2: 93.13 GiB
• Severed Steel: 93.13 GiB
• Star Wars Jedi Knight: Jedi Academy: 9.31 GiB
• Valheim: 93.13 GiB

chances are you don't have more than a few dozen megabytes of saves in any of these… so what if you could use the rest for nearly-free, general cloud storage?

Steam Cloud Drive

huh turns out this is trivially easy to take advantage of, you can just put a file into the saves folder for a game and it'll sync it

anyway i now have several gigabytes of old photos backed up in disco elysium's saves folder. if i could be bothered i'd write a script to sum all the available space across all my games and write data to it, but it's almost 4am and valve would probably ban me for it anyway