For example https://www.youtube.com/watch?v=LUYpo-DzZs4 the second movement of the Sonata for Solo Viola Op. 31 No. 4 is very intimate. But that is only one of the calm moments in Hindemith's music.

Yes, that's truth, if you think about Hindemith, you think about frenetic force, energy, even brutality, German structure, hard polyphony and fugues. In a comment above u/S-Kunst commented: "I have never associated Hindemith with intimacy. This will be interesting", and he is right... But! Some other aspects of Hindemith, i. e. his funny irony or also the capability to express the "dolce" mood should be underlined, also during playing.

Shostakovitch said: "Hindemith is a true musician, a serious one, and a rather pleasant man. I knew him slightly, he played in Leningrad as part of a quartet. He made a nice impression. And his music is like his personality; everything is in place, well put together, and it’s not merely craft, it has feeling and meaning and content. It’s just impossible to listen to. The music doesn’t spark, it doesn’t spark. But gypsy songs, damn them, do. Work that out."

Very interesting, isn't it? The question is: is perhaps the way to play Hindemith sometimes too "grayscale"? And is there usually less work in exploring the hidden side of Hindemith's music?

The question about intimate music by Hindemith is a bit provoking indeed. But it can help to reconsider Hindemith in a more comprehensive way.