Use 'ineffectual' when actions fail to achieve their goal, highlighting disappointment or frustration. Despite his ineffectual efforts, the problem persisted.
Pro Tip 2/3
Beyond Efforts
Ineffectual also implies that trying harder wouldn't make a difference; the approach itself is flawed. The team's strategy was so ineffectual that no amount of effort could salvage the project.
Pro Tip 3/3
Objective Context
'Ineffectual' is more about factual outcomes rather than someone's personal inability or failure. The new software was ineffectual in stopping cyber attacks.