Delivery via IPv6 still seems more stringent. IPv4 now requires "authentication" as well where previously only IPv6 did. Last I checked Google didn't use DANE, preferring instead MTA-STS -- perhaps understandable for a giant web property.
There is a form and people you can talk to if the form doesn't work. The form should have been mentioned in the reject message but is at <https://senders.yahooinc.com/contact#sender-support-request> though you should first review their information, rules, etc, starting at <https://senders.yahooinc.com/>, and the mailop mailing list at <https://list.mailop.org/listinfo/mailop> is where you can ask for help if the former doesn't suffice that will often result in direct contact with someone at Yahoo! that can get things done or at least give knowledgeable advice.
PiHole doesn't block all ads though it might seem to for some, and DoH (aka Private DNS) will eventually obsolete it if the amount of lost revenue doesn't remain trivial (less than the cost of implemention in their product).
You wouldn't lose the content just the ability to share it, if I read it correctly, which is something I wouldn't normally want anyway. My backups are done with restic so Google can't tell what's present since it's encrypted.
I dislike this, trend it seems, of putting the language in the URL -- the Accept-Language HTTP header should be used which can express weighted preferences. Mozilla does use the header but redirects to the language (and product) specific URL which is usually okay for me but bad for sharing (IMO, obviously). But, https://addons.mozilla.org/addon/downthemall/ "works".
If you have a (very) short list you can make/modify a search engine entry to add a -site:which.ever for each that cause problems. The problem is that the scummy sites are legion but the negate list / search term limit usually cannot handle many - I don't know what Brave's limits might be.
I believe the suggestion is to do something about the account on the other service that has been pointed to your address, e.g., if United Airlines is sending you mail about flights you never booked, perform a password recovery on the UA account thereby locking out the person that entered the wrong email address. I'm not sure I agree. But then it doesn't often happen to me.
The newsroom piece says why, it seems to me: "to better align our pricing with the value that our products and services provide.", aka because we want to make more money and we have sufficient leverage.
Privacy.com doesn't believe anyone would want their service if they have a land-line, and not a mobile. "Give us your phone number", okay, "we sent a confirmation SMS" ... hahahahaha.
Yes you can probably dodge that by going with a SMS enabled VoIP provider.