Topics in Experience Cloud in Salesforce

Topics that are created by the internal Salesforce users are separate from the Topics that are created per each community under Content Management --> Topics. External/Guest user cannot access the topics that are created by the internal users. But, they can access the ones that are created in their Experience Cloud Content Management.

Salesforce Idea

SELECT Id, Name, NetworkId FROM Topic

NetworkId is the identifier of the Experience Cloud site to which the topic belongs. This field is available only if digital experiences is enabled in your org. If NetworkId is blank/null, then they are created by internal users.