I don't particularly care to navel-gaze at the specifics of the Syrian government or Iran or Russia's failings in this humanitarian debacle when there are seismic consequences for China itself that may not be immediately apparent to many. It's bad news for China, to put it plainly, if the Syrian government has truly fallen to this lot.
It's up there as one of the biggest losers of this Salafi-Jihadist takeover and I don't say this lightly. I expect the Turkish-backed jihadist contingent to ultimately come out on top in the claim for the Syrian government's former territory because they have the full undivided external resources and support of Turkey and as such this following analysis will be assessing through that scenario. One of the major constituent factions in the jihadist coalition set to take over Syria is the Uyghur jihadist terrorists, who were basically given the role of Wagner and the British Empire Gurkas, carving a bloodbath through whichever ethnic or religious civilian population the jihadist coalition unleashed them on. All of these deeply radicalized groups were contained in Idlib and now they have most of the country to themselves, including all the military materiel and resources (including the exploitation of Syrian oil just like how ISIS overtook Iraqi oil revenue) that the Syrian government, which has seemingly evaporated, will leave behind. Even if China can somehow negotiate with this "not-Al-Qaeda" government to kick those Uyghur jihadist factions to the side, which is both a hard task diplomatically and even harder to put any faith in if there is an agreement (especially if the West subsidizes the new regime in return for requiring its hostility towards China). The only agreement that China could trust is if they disappeared off the face of the earth and I doubt there is any chance China could convince the "not-Al-Qaeda" regime to put their Uyghur jihadist co-belligerents that they've been fighting with for a decade to the shooting squad.
Another thing is that this new regime has been incidentally hugging the Turkish border for a reason, they're Turkey's creation and Erdogan's blood transfusions to the jihadists have been the only reason why they exist and why the Syrian army hasn't been able to recapture Idlib. This new offensive, more successful than I'd say even Turkey and their jihadists could have expected, is entirely the doing of Erdogan. The Turkey angle is another reason why China is among those set to lose the most. This is a Turkish checkmate for China: China had deliberately been continually allocating billions in funding for Syria to develop the country for the BRI in spite of the fact that the country has been in war-torn anarchy for a decade. The reason why China stubborning kept up with this is because developing an Iran-Iraq-Syria BRI route will bypass Turkey. There is a reason why Erdogan has been clamoring about BRICS and SCO for years and yet China and Russia have tacitly shut the door to it, they understand that Turkey under Erdogan and under NATO alignment is fundamentally unreliable. This means that China's BRI in the Middle East will either have to pass through a Turkish-aligned "not-Al-Qaeda" Syrian regime or through Turkey to reach Europe.
Turkey had been pushing for a "Middle Corridor" of Turkmenistan-Azerbaijan-Turkey BRI route because while this would be satisfactory for China's BRI goals, war-torn countries like Iraq and Syria were actually still preferable for China compared to staking its vital trade route (which was designed as an Eurasian lifeline in case of maritime blockade) within a literal NATO territory like Turkey. Furthermore, the Middle Corridor is Erdogan's grand strategy of using China's trans-national infrastructure project to parasitically bind Azerbaijan and the Central Asian countries economically to Turkey for the sake of his "Pan-Turkic" fantasy. This fantasy will be given a boost for Erdogan's ego now that he will seemingly subordinate Syria as a Turkish lackey and it will now be something that China will be potentially entrapped to build for Erdogan. Extending the scope of Turkish influence into Central Asia through the Middle Corridor BRI route will inevitably also advance its cause of infiltrating Xinjiang. Still a fantasy so long as China maintains vigilance on its end but still it is undeniable this regional shift will advance it unless the "not-Al-Qaeda" regime breaks with Turkey and eliminates the Uyghur jihadist terrorists, which is quite unlikely. In any case, the Central-Asia/Pakistan-Iran-Iraq BRI option has been sunk for China and building the Middle Corridor is now seemingly a choice of no choice.
As for the West, it has seen how Salafi-Jihadists will target it and I doubt they will make the same mistake. Likely, they'll dangle funding and recognition of the new regime if the jihadists point their sights elsewhere. Trump's first presidency was when the Xinjiang atrocity propaganda was fully adopted by the US as state policy and so I expect he'd have quite some synergy of aims with Erdogan. China will do its utmost to make the best of the situation but this is indeed an unpleasant outcome for China.
You are vastly overestimating the impact this has on China.
Uighur jihadists in Syria is as much of a threat to China as they were in Libya and far less then when they were in Afghanistan.
As for connecting to Europe via land, well I think China’s interest in that has cooled significantly since the Ukraine War. The EU has demonstrated in no uncertain terms that they are US vassals who will happily flush their own economic interests down the toilet to please America. Why spend all that money building land links to Europe when they will NordSteam it all at the first command from America?
BRI’s primary objective is to create new markets in the global south linked to China’s economy to allow China to shift exports from the U.S. and EU. The secondary objective is to provide land base access to ME oil. None of that has anything to do with Syria.
Syria only matters from a geopolitical POV because of Israel. That’s never been China’s concern.
China’s reaction to Syria is, ‘Pity, but anyways’.
The biggest looser in this is Iran and Hezbollah. As now Israel and America has one less obstacle and more assets to use against them. Their biggest mistake was in not securing more concessions from Assad to better safeguard against this eventuality rather than continue to let him run things, when he has already proven he was ill suited to the task.
That’s the problem with having vassals and proxies. You either end up having to step in yourself to make sure things are done properly, or you risk getting rolled when they do a shit job on your behalf. And vassals and proxies always end up doing a shit job because they just end up relying on you to bail them out when they fuck up.
This is why China doesn’t pick sides. They see who has the power, disciple and resolve to win, and then work with them. If the winners are not to China’s tastes, then China doesn’t need to work with them at all. If they want to do business with China, then they need to make themselves less hostile to Chinese interests. The Taliban learnt that quickly enough. I don’t see why the Turkish backed head choppers will be any different. And if they do decide to act against Chinese interests irrationally, well then they will have earned all of their enemies some support from China.
It’s easy for China to play this game because it is not already entangled in it. That gives China far more space to manoeuvre, clarity of prospective, and time than all the other parties stuck in the middle of it.