ico you can check if it is enabled for the site you are on by tapping the slider icon on the left side of the address bar.
Under 'Permissions' it will say ads blocked.
Bear in mind it isn't going to be blocking every ad in sight. I imagine this has been / is quite a difficult thing to decide on for the devs as they have to choose a list / lists that do not break too much functionality and also do not make the general vanadium fingerprint too unique. That would also be one issue with allowing custom lists, among other issues.
You can use this website to test if adblocking is working (make sure your DNS adblocker is disabled temporarily when you check) around 60-70% is a good indication of adblocking working. It is not meant to be a race to get to 100% (even the dev of that website says it is just to indicate whether your blocklists are working).
It is a balance between blocking some ads and trackers, not breaking too much functionality, and maintaining a similar fingerprint among vanadium users (because you can be tracked across different sites via your browser fingerprint, this is becoming more common as third party cookies are phased out). Blocking every single ad you can may have the reverse effect if evading tracking is your goal. Here is an example of browser fingerprinting - if you have a different identifier each time then you may not have been tracked but, also, if you have the same identifier as other vanadium users, that is good as well as you are 'blending in with the crowd'. It is just an example website, there are probably better ones out there. Also bear in mind fingerprinting is used alongside other forms of tracking in practice.
Apologies if I'm wrong in any area. It isn't simple (at least not to me lol) and I don't envy the GOS team trying to implement this while people start wanting everything to be blocked or to use custom lists.
EDIT: I don't speak on behalf of GOS obviously, just speculating about how it might be a difficult choice for them to make by putting myself in their shoes, though of course they are a lot smarter than me :)