Chatter remains a very popular use case for Act On It, and one of the simplest to set up.
Locate the Chatter Notification message type, activate it, and @mention yourself to see messages appear instantly in the inbox.

That said, every business uses Chatter slightly differently.
You might want to:
This article shows you how to adapt Act On It so Chatter notifications behave exactly the way your org needs.
Act On It has two Chatter-related flows, visible under Setup → Flows:
Act On It - Notify Users @Mentioned In Chatter
Sends a notification when a user is @mentioned in a new post.
Act On It - Feed Comment Trigger Flow
Sends a notification when someone comments on a post the user created.
Flow Templates
You’ll also see two similarly named flow templates. These are editable versions of the packaged flows and are intended to be used as starting points for customization.

The packaged (active) flows are locked because they’re part of the managed package. Your customized versions will be based on these templates.
If you want to tailor the Chatter experience:
1. Deactivate the packaged flows
This ensures Act On It doesn’t use the defaults.
2. Create new editable versions

For each template:
Salesforce does not support Feed Comment events with record-triggered flows. To handle this, Act On It includes a small Apex trigger that hands the event off to your chosen flow.
To connect your custom flow:
1. Copy your flow’s API name
Open your flow → Details & Versions → copy API Name.
2. Update Act On It Settings
Go to: Setup → Custom Settings → Act On It Settings → Manage

Edit the settings and paste the Flow API name into the 'Feed Comment Flow Name' field.

From then on, when someone comments on a post, Act On It sends the comment details into your flow and your logic determines who is notified and how.
By replacing the packaged flows:
Chatter becomes a fully customizable notification channel, aligned with your organization’s processes.