Hi there,
Just to be sure, check under WP Admin ? WooCommerce ? Settings ? Accounts & Privacy, that you have Allow customers to place orders without an account checked:

If you do have that checked, and your guests still need to log in, then it could be one of the following reasons:
- A theme or plugin setting is overriding the functionality.
- Your guests are trying to purchase a product type that requires a login regardless of that setting, like a subscription product.
If it’s an issue regardless of the product, then temporarily swap out your theme for a standard theme like Storefront, to check if it’s a theme issue. If not, a a conflict test could highlight which plugin is causing it.
You can also reply here with your System Status Report, in case that could shed more light on this issue. To find it, go to WooCommerce ? Status, select “Get system report” and then “Copy for support”.? Then paste it here in your response.