There is no universal answer to this question. However, there are genres that are more suitable than others. Accordingly, these music genres are used more often in documentaries. However, there are no limits to your creativity. In each individual case, the visual or audio material decides - the royalty-free music tracks on audiocrowd.net are also suitable for radio documentaries.
Music for reportages or documentaries always takes over a certain task. Besides supporting the atmosphere of the visual material, music serves to create a dramaturgy. With the help of the right music, you can support the suspense of your documentary in a subtle yet effective way. For example, certain pieces of music create a sense of departure, others build tension, and still other pieces release that tension. For the sense of departure, an ambient piece with a soaring melody might be appropriate. A scratchy, nervous rhythm builds tension and a harmony-driven song discharges that tension again. Accordingly, music on the subject of documentation does not consist of only one particular genre. Thus, the mood described in each case is helpful as a clue. Examples are: dreamy, exciting, happy, inspiring, etc.
Also, you can use this royalty-free music for documentaries to structure different sequences. For example, if the sequences were created in two different locations, "each location" could have its own music. In this way, the music can support the editing. Thus, music for reportage helps structure and assemble the footage. Other pieces are ideal for a voice-over. So there are different ways to use music in documentaries. Thereby music for reportage takes over different tasks.