If you wanted to describe Trump’s Syria policy in one word, it would be “indifference.” Trump didn’t have the slightest interest in the geopolitical implications of the conflict or the vast misery that resulted from it. He just wanted to get America out of the picture as soon as possible. If Putin and Erdogan were determined to make deals and run the place, so much the worse for them.
Biden won’t be oblivious to the situation, but don’t expect him to make any dramatic changes in American policy. He probably won’t withdraw the handful of troops we use as a tripwire to maintain some minimal leverage there, but he won’t intensify our involvement, either. It is simply too late for that.