To bugger all means to do nothing or next to nothing, and in this sentence the person spent an afternoon in a bath that did nothing to help them.
Context: "I spent the whole afternoon in a bath full of tepid water that was supposed to help and did absolutely nothing." Claim: "I spent the whole afternoon in a bath full of tepid water that was meant to help and did bugger all."
Considering the context, is the claim true, false, or unknown?