Game download blocker
On option would be to minimize the displayed ads using an app like Blockada (not available on PlayStore).

This app filters out ads and app trackers using filter lists that clock certain requests. This usually reduces the number of ads.

A second option would be to use the multi-user system on Android (if it is available on your device). Additionally to the primary user you can create a second user which is not able to install any app. 

The third option would be the Google parental control system which is AFAIK able to block certain app installations. Just switch "parent" and "child" while reading ;)