GlytchMeister Vanadium doesn't support extensions and Manifest V3 was never designed to prevent ad blockers from working, it simply aims to reduce elevated privileges and give developers ways for users to have better control over what the application can access, which is a good thing on the paper, better a less strict block than full access to all your websites, ad blocking isn't really a privacy/security feature, but more for convenience, it only blocks low-hanging fruit, requires trust in lists and can be compromised, discussions in more or less obscure forums, under the guise of open-source, of what should and shouldn't be blocked isn't anodyne either.
In fact, It's always possible to develop a malicious application under Manifest V3. Of course, this is a caricature, but it's not impossible - in general, browser extensions pose problems (I use some of them).