This ist just PR. The al-Tanf rebels know that they lost and they will stay there until a final deal will be made.

Exactly. They spoke about breaking the siege of the east Qalamoun pocket and even that of east Ghouta pocket. Both no longer exist today. They were originally supposed to march on al-Bukamal and even boasted of going to take Deir-ez-Zor. Both are firmly in Syria's hands today. So all they can do is these kind of stunts marching in circles on sand for the camera. The only ones holding that territory currently are the U.S. airforce.