Consider donating clean plastic plant pots to plant enthusiasts. Some pots could also be sold. If they’re in good shape try selling or donating them on an online marketplace such as Facebook Marketplace, Craigslist, OfferUp etc. Some thrift stores might accept them. You can try calling nearby thrift stores to see if they’re accepting them. You can also place them outside with a free sign. Especially in spring they will be taken right away.
Many local recycling programs accept clean plastic plant pots. If you’re local recycling program doesn’t accept them, plastic plant pots can be recycled at many Home Depot and Lowe’s stores. Look up specific store location on the store’s website and it should show if they take plastic plant pots.