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Solution
BTW, you can try working around it by changing the mod's versioning (assuming the mod doesn't affect things which were changed from 1.35 to 1.37.5).
Yeah it really depends on what mod it is exactly. Music or graphical mod might be fine, but any kind of overhaul mod likely won't work across versions. You're better off looking for a version of the mod that works with the current version, if it's an overhaul.

For OP, Steam is pretty much the way to go unfortunately. Old versions going back to 2016 are still on there.