This look can be made with a mix of capture technique and post-processing.

For the diagonal blur, you can either:

• create it in-camera by moving the phone slightly during a long exposure, or
• add it later with a directional/motion blur filter set to a diagonal angle.

For the smooth, painterly effect, the answers suggest using smoothing filters such as a median-style filter, which evens out areas while keeping edges relatively defined.

In this specific case, the photographer said it was shot on an iPhone with the SlowShutter app, then processed in iColorama and Brushstroke, and blended in SuperimposeX. So the final look likely comes from:

1. a slow-shutter capture,
2. some intentional camera movement or added directional blur,
3. painterly/smoothing processing in apps,
4. blending multiple processed versions together.

If you’re editing on desktop, a motion blur plus a smoothing/median-type filter can get you close. On mobile, apps that offer painterly effects and layer blending are the key.