Tethering - is it possible to "turn off" the Internet on the distributing device?

Question

Android

There are two devices - a large powerful tablet and a mid-range phone. Both devices are Android.
One of the main functions for which the phone was taken was the distribution of the Internet to a tablet devoid of the joy of LTE (at one time I had to save money and buy a Wi-Fi version of the device).
I use the "Modem Mode" function all the time, but there is one drawback: when the phone shares the Internet with the tablet, it continues to receive all and all notifications from applications, engage in unnecessary synchronization, etc. Although such functionality in the "modem for tablet" mode is clearly not required of him.
What is the risk? Parasitic traffic is chasing (up to twice), as a result of which the effective available traffic and the effective Internet speed for the tablet are reduced.
I would like to have a "router" type mode, in which the phone forgets that it is an independent device itself and uses LTE solely to transfer it to a "paired" tablet.
A cursory googling turned up nothing. The option to "turn the phone into a permanent modem", removing everything from there in general except for system services, does not suit. Disabling all kinds of synchronization every time and nailing all messengers is very tiring. Is there any ready-made solution for such a case?

Answer 1

Disable background data transfer in system settings.

Answer 2

root the phone and disable direct traffic in the firewall, only allow forward traffic