The manifest v3 changes primary give a lot of security and privacy changes that stop extensions from doing a lot of questionable things in the background on all your page you visit. But that does stop ad blockers from doing a lot of what they currently do - blocking in page elements and modifying the pages you visit.
It also killed a lot of other genuinely useful extensions.
And if security is their main concern they should have spent resources on making sure the extensions they themselves redistribute are safe, not on killing a huge chunk of extensions. Sorry but you’ll have a very hard time convincing anyone that getting rid of ad blockers wasn’t their primary motive.
But it does not block them from blocking page requests so ad blockers like ublockorigin lite can still function in a more limited capacity to block ads.
It completely changed how they do this, and made it way less effective and more limited. All completely unnecessary from a security standpoint.
Hopefully noone, so it would lead into more fragmentation in the browser space, which is a good things.