Please check the following to determine why the product page’s Add to cart button doesn’t show up:
- Check if store is in catalog mode in Customizer > WooCommerce > Product catalog > Misc. options eg: https://d.pr/i/MPfggU .
- Check if the ATC button is disabled in Customizer > WooCommerce > Product page > Components in Summary > Add to cart block eg: https://d.pr/i/pB9lXb .
- Check if the Buy Now button replaces the ATC button eg: https://d.pr/i/J0iXeH .
- Check if the product is in stock, or purchasable;
- Disable other plugins to see if there might be some conflict involved.