Does the EU withdrawal button apply to my WooCommerce store if I only sell B2B?

Only if you sell exclusively to other businesses. Directive 2023/2673 amends the Consumer Rights Directive, which applies to B2C transactions — sales to consumers. If your WooCommerce store is pure B2B (no consumer customers at all), you are not covered. If you sell to a mix of businesses and consumers, the requirement applies, you need a withdrawal flow available to your consumer customers. Many mixed stores assume they are exempt because most of their revenue comes from business clients. That assumption is wrong.