On my Oneplus Nord Avicii I kept the configurations to block any LTE traffic and also setup limits of 0MB to avoid all and any traffic through service provider and only allow it through Wi-Fi. However on 2 occasions I was charged for a residual traffic that happened of 1Kb.
It might be a real pain for the development team to figure out where that 1Kb comes from but the only thing I could relate to it is when I manually set it in airplane mode. But this isn’t 100% sure because I do it almost every day and only twice this month this was charged so some minor leak somewhere not easy to spot.
I can live with this limitation because the provider already offered to block Internet traffic from my phone number but I tend to believe this traffic is due to some minor leak in spite of the setup I have blocking Internet traffic through the provider and allow only through Wi-Fi.
NOTE: the advanced privacy was disabled in both ocasions.