Using Google Tag Manager doesn't mean you are using the server-side tagging. You have to configure it in your account. It is something you have to pay for. If you read the instructions on https://developers.google.com/tag-platform/tag-manager/serve... you have to have GCP billing setup to pay for the App Engine instance running the server-side tagging proxy.

thx for the explaination, btw, do you think server side GTM can let Adsense bypass the adblocker, since it is what claimed in the article. Though after Googled a bit, I can't find a single article/video about this.

Somewhat. Some of the tracking protections center around 1st party vs 3rd party. If the site owner takes the time to configure the DNS records for this server-side proxy then the page is only communicating with 1st party domains so that protection is gone.

Next, ad blocker components often target various parts of the URL. By hosting on your own domain the domain name matching patterns that would be used for blocking no longer apply. But the ad blockers can also use just the path or file name portion of the URL to block on.

Easylist has a set of lists that are commonly used by ad blockers such as UBlock Origin. The tracking/privacy centric list is https://easylist.to/easylist/easyprivacy.txt which I'm using in UBlock Origin. If you look at it there are lines like '/gtag.js' which might match on the name of the JavaScript file and still block it.

Of course site owners might change the name of their script files to a non-default name making it harder to detect.

The next step in the arms race would be having more dynamic names for the files and URLs. You could rotate the names of the scripts and endpoints automatically at which point the adblockers would have to preform content inspection or some other strategy which is more resource intensive.