The party says existing policies have failed to bring the disease under control.
Rhun ap Iorwerth pledges greater cooperation after Labour and Reform sink government spending plans.
Welsh ministers say the existing settlement "does not cater to the realities" of UK devolution.
Plaid Cymru needed help from another party but could not agree a deal on its spending plans.
Plaid government says changes at South Wales Fire and Rescue Service not yet sufficiently embedded.
The Plaid Cymru-led administration is hoping to strike a deal to pass its supplementary budget on Tuesday.
The first minister will meet a UK government minister for the first time on Friday.
Concerns are raised about negative impact on existing benefits, with UK government agreement needed.
Plaid Cymru lose vote as Reform, Labour and Tories team up to defeat the party over schools funding.
