looks like rendering adblockers extensions obsolete with manifest-v3 was not enough so now they try to implement DRM into the browser giving the ability to any website to refuse traffic to you if you don't run a complaint browser ( cough...firefox )
here is an article in hacker news since i'm sure they can explain this to you better than i.
and also some github docs
Doesn't not being able to modify it would also imply that the information can not be parsed? Thus this consept falls apart immediately as the information would need to be able to be parsed so that it can be rendered?
The browser would need to be allowed to parse it, as they're the ones displaying the content; it would imply, however, that adblockers and other extensions would no longer be allowed.