You’re describing the classic symptoms of a near-dead battery. Lights, radio, horn, AC fan, etc, only need 12 volts to work, which the battery still has, so they still work.
Starting the engine takes AMPERAGE, which your battery no longer has enough of. Ask someone to “load test” the battery. If it passes I’ll be amazed.
If this is the original battery it’s just one more indication that it’s time for a new one.