Yes. In the plan, under the products you selected, tick Only sell selected products as subscriptions. The widget then shows the subscription options alone and the one-time price disappears from the product page.
Read the help text under the checkbox before you save it, because the setting can be wider than it looks. With Mollie checkout on, it says Hides one-time purchase for these products in the subscription widget. Without Mollie checkout, it is a Shopify product setting, so it applies to the whole product, including variants outside this plan. With Mollie checkout on, the app saves it for the widget instead and clears Shopify's own product setting. If the products you picked currently disagree, the form warns you that they use mixed Shopify settings and that ticking the box applies one value to all of them. "Sell a product on subscription only" goes through it step by step.
Stuck on any of this? Open the chat in the bottom right corner of the app and we will help you set it up.