A knowledge article written and published is searchable in normal UI but inside Service Portal the same knowledge article cannot be found when searched.
Istanbul, Jakarta, Kingston
In Service Portal, by default, only one knowledge base is configured to be searched, unlike the normal UI where the search engine searches from all the knowledge bases.
Check whether the knowledge article's knowledge base is the same as the one configured in the Service Portal knowledge base.
To link multiple knowledge bases to a Service Portal, you can add a new Search Source for the other KBs so they will be included in Search results if any articles match) and then clone and customize the knowledge base widgets (for example, KB categories) to include the other knowledge bases.
See the following Community articles for more information: