Which of these could cause cross-contamination when preparing food?

Different cutting boards should ideally be used for preparing raw meat and vegetables. At minimum, the board should be thoroughly sanitized in between the two preparations. As long as all bread cut on the board either contains gluten or is gluten-free, this shouldn’t cause cross-contamination. Note that ever-changing allergen guidelines may require additional restrictions with regard to gluten, nuts, and other allergens during the food preparation process.