Well, Russia was really supporting Syria, as Syria was a client state of Russia. The U.S. has had a few incursions in Syria since 2013, mostly under Obama, and a little under Trump. But Russian troops were mostly given free reign.
Maybe so, but our stated purpose in Syria was to ‘fight the terrorists’, which was EXACTLY what Assad was trying to do, so it looks as though we didn’t help him much. You know what they say: “With allies like that, who needs enemies.”
Only dummies or tools (neither of which you qualify as) lump together all the anti-Assad forces as terrorists. The Kurds can be themselves split into 3 groups, with the YPG tabbed as terrorists by Turkey (at least some are) but the majority of Kurds are not terrorists despite being opposed to Assad. Hostilities between the Kurds and Syrian Army forces have been modest recently (for this region, anyway!) with Assad content to let Hezbollah* and Iranian backed militias from Iraq attack the Kurds in the East; Turkish forces and Turkish backed groups attacking the Kurds in the North.
Don’t get me wrong, the Kurds hate Assad, with good reason, but, they don’t seem to have any designs on Damascus themselves. Most indications are that given a reasonable settlement of territory, significant autonomy, and no attacks on them by Assad or his backers, Assad would have had little to fear from the Kurds. The Kurds would still have their hands full with AQ, ISIS, and Turkish backed forces. HTS would be a question, but HTS controls little territory directly bordering Kurdish areas anyway, and an uneasy truce between HTS and the Kurds would make a lot of sense. Neither can really afford to be fighting the other. Similarly, HTS and the Kurds making clear they have no hostile intent toward Israel makes a lot of sense for those 3 parties. Granted that such a “partial solution” is a long shot. 1 in 5 at best(?), and even then, that assumes maximum cooperation in keeping Hezbollah stomped.