Single Google Tag Manager is, in fact, a tag manager, it can be used to load other integrations and analytics tools, such as Intercom, RocketHub, or Google Analytics.
Configuring tags and triggers
To configure custom triggers based on specific events, open Triggers for the GTM container integrated with your flow (from Google Tag Manager, not Formsort).
Choose Trigger Type: Custom Event. Choose an Event name corresponding to a Formsort event (ex. FlowLoaded, StepCompleted, etc.).
Under NewTags, choose some type tag in Tag Configuration, like Custom HTML Tag.
Configure your Triggering event, and then publish the container via Save.
Now, head over to the Integration Tab in your flow, and add the Container ID to the GTM integration setup.
The Enabled events options control the events within Formsort that are sent to GTM as a dataLayer.push. Note that, as long as a Container ID is provided, GTM will always be loaded, and any of the analytics events you enable will be sent to Google Tag Manager (i.e. FlowLoaded, FlowClosed, etc).
The shape of the payload will also be configured and can be previewed at the bottom of the menu. Choosing to Send answers will allow you to push answers to GTM as well.
Append StepID to StepLoaded and StepCompleted event names will add the Step ID to the payload when you receive a StepLoaded and StepCompleted event.
If you have deployed flows previous to integrating with GTM, it is advisable to re-deploy those flows.