Short answer: No—avoid Biscoff (and any packaged biscuits) during Paryushan.

Why:

• Paryushan maryādā keeps food very simple: no fermentation/yeast, no outside or long‑stored/processed items, and no “taste-seeking” snacks. Biscuits are factory‑made, stored, and typically include raising agents and multiple processed ingredients, so they don’t fit the spirit of austerity and ahimsa.
• Eat only fresh, simple, non‑root, non‑leafy, non‑fermented food in daylight; drink only boiled/filtered water within the allowed time.

Tradition notes:

• Shwetambar (8 days) and Digambar (Das‑Lakshan, 10 days) both keep food simpler than usual; packaged snacks are generally avoided in both. Follow the specific pachchakkhān (vows) given by your guru/saṅgh.

Better choices:

• Fresh, same‑day simple preparations (grains, dals, non‑leafy/non‑root vegetables), or plain fruits if your vow allows, only in daylight.

For easy guides:

• What can’t we eat in Paryushan
• Food items allowed in Paryushan
• What to eat during 8 days of Paryushan