Windows and System Update data consumption

Pausing Windows Update, setting the connection as metered, and turning off Delivery Optimization can reduce data usage, but they do not necessarily/completely stop Windows from using data.

Windows can still download things like Defender security updates, some critical updates, drivers, Microsoft Store/system components, and other background system files.

Also, turning off Delivery Optimization only stops Windows from sharing/downloading updates from other PCs. It can still download directly from Microsoft.

I would suggest that you check Settings > Network & internet > Advanced network settings > Data usage and see how much data “System and Windows updates” is actually using.

Also check:

Settings > Windows Update > Advanced options > Download updates over metered connections

Make sure that is turned off.

As a practical next step, reset the data usage statistics, use the computer normally for 24 hours, then check which category is increasing. If “System and Windows updates” still uses several GB, check Windows Update > Update history for failed or repeatedly installed updates, as that can indicate something is being downloaded repeatedly in the background.