Three actions that are applicable when modifying the number of steps required in the Salesforce Commerce Checkout flow are:

Perform a template override on the Checkout page. This action will allow you to change the structure and content of the Checkout page, such as adding or removing sections, widgets, or fields. For example, you can override the checkout.handlebars template and modify it according to your requirements.

Set the value of the configuration setting defined as CO.overrideFlow to TRUE. This setting will enable you to use your own custom checkout flow instead of the default one. You need to set this value to true before you can modify the checkout flow.

Set the value of the configuration setting defined as CO.useDef to TRUE. This setting will enable you to use a single-page checkout flow instead of a multi-step checkout flow. You need to set this value to true if you want to reduce the number of steps in the checkout flow to one. Salesforce References: B2B Commerce and D2C Commerce Developer Guide, Checkout Flow