This is kind of where I'm at. Almost all media has gone click-bait because controversy is what stirs readership. My opinion is that Trump's mental acuity is a greater question than Biden's, but that both are sus.
I really think there's a case to be made for an age-out of at least state and federal officeholders, but more tied to term limits. A comment that has stuck with me from an 80-year-old that was on my comprehensive plan committee probably 10 years ago... "my opinion on what I want for the future of ________ is not as important as yours... I'll be dead, but you'll get to live it." She later shared that she thought it was irresponsible for the City Council to appoint her to the committee. As people age into their late 60s and 70s, I think they begin to lose that long-term perspective as their sense of mortality sets in. This isn't to say their opinions cease to matter, but it does become a legitimate question as to whether they can/should represent others. Of course, the clean way to solve most of this is with term limits, including for SCOTUS.
I don't like Kamala Harris, but as you said she is light years better than anyone Trump will tap. There's probably better than 50/50 odds of death while in office for both in a '25-'29 term. We haven't seen a VEEP ascension since Gerald Ford, and even that was a really strange set of circumstances. You'd really have to look to LBJ.