Perhaps it is late for this answer but in the PrimeNG docs this can be found:
https://primeng.org/button#template

  <p-button [outlined]="true">
    <svg width="35" height="40" viewBox="0 0 33 35" fill="none" xmlns="http://www.w3.org/2000/svg" class="block mx-auto">
        <path d="..." fill="var(--primary-color)" />
    </svg>
  </p-button>