Canada

The NDP, despite being tiny in the last two governments, enacted some of the biggest (incremental) changes this country has seen in recent decades. Dental care, pharma care, small rental and housing affordability improvements, universal sick leave protections, etc.

They clearly were the policy "winners" in the last 4 years, whether you agree with the initiatives themselves or not.

They were completely ineffective in the rhetoric and self-advocacy space, where the Conservatives clearly won (whether we find this agreeable or not). This is in part due to the fact the NDP can only get soundbytes on mainstream media access when it's subjectively on things no one else is talking about, making it look like their priority, and in part due to the fact Canada has a major American Republican media arm reaching into Canada (and the slow pivot to inexpensive influencers who hammer the same speaking points effectively as "common sense").