Publishing a report in Reports > Library > Collections means that:

Publishing a report in Reports Library Collections in GA4 makes that report accessible to all users who have access to the specific GA4 property. It doesn't make the report publicly available to anyone with a GA4 account globally, but rather to those within your organization who have been granted access to your property. This allows for standardized reporting across teams. The report does not start collecting data at this point; data collection is configured independently through tags and events. This step is unrelated to activating Publisher ads reports. While publishing does make the report appear in the Reports menu for other users, the primary implication is its availability and sharing within the property's user base.