One of the rules of the peace agreements was: No new recruitment, no campaigns.

Now instead of SAA they try to avoid the deal by pro-SAA "PMU".

Not in Qamishlo city itself but in the villages South there is a power struggle between Arabs. Some pro Regime but others want to have more say. They look to YPG/SDF for options. But YPG/SDF wont do anything unless they have a reason to act. Previously reasons to act were breaking of the agreements or NDF acting weird.

I don't think anyone is "forcing" the Arabs to stand up against the Regime. The claim itself makes no sense on the military strategy level. But it could be that they are putting out the messages that they'll allow Arabs from Regime-held territory to join their ranks instead of "PMU".

Note: you can cross from SDF-held Hasakah into Regime-held Qamishlo, chat with Regime / Pro-Regime soldiers, take a selfie with an Assad statue and watch football in a bar. On some "fronts" in this area those who man the checkpoints are friendly with each other, in other areas not so much. Could have many different reasons, Im not sure why at some places there is more hostility and at some its friendly.