I'm not really aware of what's going on in Syria, and not really sure who's worse - Assad or the rebels, but it seems clear that Iran & Russia, which were main backers of Assad regime, appears extremely weak. That's understandable for Iran which may want to avoid to overextend itself following the recent events, but it's hard to comprehend why Russia was unable to do anything at all. In any case, it seems like there…
The dust hasn't settled, but my assumption is that the Russians had a sort-of working plan that the Syrian army would do the heavy lifting and Russia would be funnelling in supplies and providing power for key points - following a proxy-war style defensive model. Given the speed and totality of the Syrian army's collapse they didn't really have anything to do that wouldn't be hideously draining on resources that they don't really have.
The collapse of the Syrians may be related to the Russian military being distracted by the Ukraine war in an indirect or direct way. My base case guess is the Turks/Turk-backed faction spotted an opportunity while the Russians were distracted and went for it, and the Syrian forces were complacent because they hadn't really prepared for the situation where Russia is in a war elsewhere.