There is a difference between having an auto OS and having one capable of L3/L4 autonomous driving. For something L2 or lower, the requirement is low enough that most automakers can probably develop their own system.
If BYD gets banned, CATL and gotten and others will get banned too. Western automakers will get banned from China. With Huawei, Western government can use the national security argument. The most they can say about BYD is economic security. Aside from America, that line is not going to work anywhere else. BYD is already shipping over 1000 cars to Australia and NZ. It will probably build plants in Europe (Hungary or Poland) and have no issues in EU market. Frankly, countries like Hungary and Poland would rather build foreign cars in their country than just accepting them from Germany.
Remember, people (at least the liberals) like BYD for it being a major player in the fight against climate change. Huawei has basically no admirers anywhere in the West.
There were rumors a year ago that Song+ EV will use Huawei motor, but there has not been any evidence of that in action. In fact, Song+ platform is pretty much only selling DM-i models at the moment.
Huawei does not produce Lidar, ultrasonic radar or the megapixel camera. It also currently does not produce the SOC that are used to power autonomous driving to the best of my knowledge. Pretty much all of the Chinese automakers are invested in Horizon Robotics.
Huawei will probably work something out with all the legacy Chinese automakers to supply them this solution. That's why BYD would regard Huawei as a major competitor. If you are BYD, you do not want to have inferior product to Huawei, since that means your own cars might be worse than Geely or ChangAn produced ones.
As I said above, this CATL/Mercedes news is huge. a 100 GWh plant for Mercedes and probably BMW would cover a good chunk of EV production from those 2 automakers. I'm sure they will eventually add even more plants by 2030 (assuming geopolitics don't change). Chinese battery makers have the entire European automaker market locked down. LG Chem and Panasonic are basically only able to get deals in America.
Big news for Geely as it owns about 10% of Daimler AG.