So. Server-side gtm is exactly what it says. It's executed on the server. It listens for network requests. It doesn't have any exposure to what happens on the front-end. And the front-end has no clue about there being a server-side GTM. Well, unless there are explicit calls to its endpoint, which you can proxy with your backend mirrors when needed.

What you experience is adblockers blocking your front-end GTM container. Even though it's theoretically possible to track all you need, including front-end events with server-side GTM, it's considered to be the best practice to use both GTMs and stream front-end events to back-end GTM through front-end GTM.

This, of course, makes you dependant on adblockers since they will block your front-end GTM. A way to avoid it is... Well, not to use the front-end GTM and have all your tracking implemented either in a tag manager that is not blocked (I doubt there is one) or just have your own custom javascript library doing all the front-end tracking and sending it to the backend GTM to be properly processed and distributed.

Generally, it's too expensive to implement tracking with no TMS, since now you really have to know your JS, so only the cool kids can afford to do this. A good example would be Amazon.

Basically, it would cost about two to five times more (depending on particulars) to implement tracking with no TMS, but adblockers typically cut only about 10% of traffic. 10% is not vital for reporting, measuring effectiveness of funnels and what not. All the critically important data is not being reported on by analytics anyway. Backend is the real source of critical data.

You can easily do this if you use sGTM hosting from https://stape.io There is a feature called Custom Loader. With it, you can download Web GTM from different paths and all other related scripts will be also downloaded from different URLs, for example, gtag.js for GA4.

More info https://stape.io/blog/avoiding-google-tag-manager-blocking-by-adblockers

You can also create your custom loader client for Web GTM. However, there will be problems with related scripts. UA/GA4 still will be blocked then, but GTM itself not.

So, I finally implemented a great solution using GTM client templates. It works like a charm.

To summarize, the steps are:

1. Create a client template from your server container. You can import this template from https://raw.githubusercontent.com/gtm-templates-simo-ahava/gtm-loader/main/template.tpl
2. Create a new client from this client template
3. name your path as you want

This article explains perfectly the required steps: https://www.simoahava.com/analytics/custom-gtm-loader-server-side-tagging/