Yes, once a collection has been added to Foundation, NFTs can be listed on the secondary market. Here's how:
Visit your profile page.
Click on the "Owned" tab.
Find the NFT you would like to list for auction.
Click "List" on the artwork card.
In your wallet, sign the message to approve that you want to list your NFT in the Foundation auction contract.
Add a reserve price.
List your work for auction.
Once you've completed the above steps, you will be able to check from your profile whether the NFT has been successfully listed on the secondary market.