Apple Intelligence-powered natural language / semantic search in Photos on Mac

Using Photos on Mac running MacOS Sequoia 26.1 and the latest version of Photos, and have Apple Intelligence & Siri turned on in System Settings. Photos now supposedly supports natural language and semantic search, e.g. “Photos from my most recent trip to Germany” or even something simpler like "Rome monuments", but these and other even more straightforward searches draw a complete blank. Only the information from keywords, title etc. - which is what the old Search function also used - seems to work. How to get AI search working?