Oneplus & Moto are pretty clean for Chinese, just saying.
If you say about nagware like those push notification ads, guess what, Samsung M series has them as well & they can only be reduced a lot during first setup. I have a feeling that if my S20 FE was setup by someone other me, it will push some suggestions notifications as well. In MIUI, at least you can disable those post first set up as well. Most local shopkeepers always check all boxes when setting up your phone for the first time. I recently tagged along with a friend who bought an Oppo (not a good decision, I know), I literally had to snatch the phone from the shop employee's hand at Poorvika.