Not sure what are you talking about. Chinese smartphones companies have their own app system that Google has no control whatsoever. If Apple wanted to ban Douyin, then Apple is finished. Last time Apple tried to go against Tencent, it folded very quickly because users have threatened to abandon Apple for Wechat. Beside, the Chinese government would ban Apple if it tried something like this.
Huawei has never had any problem selling it smartphones in China with its own system. It is the ban on chips that caused Huawei to lose the ability to produce top tier phones.
Chinese mobile devices (outside of Apple) rely on Android derivatives, do they not? Google has a high degree of control over any Android platform that isn't actively being developed as a fork (like Harmony OS), because core Android updates come through them. Chinese companies like Xiaomi, Vivo, and Oppo do consumer side customization of the platform, but they do not do core Android platform development. If the US bans access to Android updates, it's going to be a huge blow to any of those individual companies.
The US is smart enough, as I said above, to not do a country wide ban on Android because they prefer to channel resources into "useful idiot" companies. So say they wanted to target Xiaomi - they could just cut that company's access to Android updates, while still allowing it to Vivo and Oppo, causing the latter to gain a competitive advantage because they'll be able to benefit from Android platform upgrades while Xiaomi would be stuck with an older version with all the attendant bugs, security vulnerabilities, and feature deficiencies.
This is part of how they targeted Huawei; of course, the other arm is the chips ban, which works the same way, but with a higher barrier of entry.