John Quincy Adams went on to become a Representative for MA in the House and I'd argue was the only real demotion post-presidency.
William Taft went to the Supreme Court after his Presidency (not exactly a lateral move in and of itself) but was the Chief Justice so it's probably close. Then again institutions powers wax and wane over time, so it could be argued that it was a demotion.
Lastly, kind of a bonus factoid of post-presidency activity -- Teddy Roosevelt, after serving a term plus some (edit: he took over the presidency as the VP after McKinley's assassination) and was a Republican. He later ran in 1912 as a candidate for the Bull-Moose Party after a rift in the Republican party when they nominated the above W. Taft instead of himself or another more Progressive Republican.
Thankk you. The Overton window has been forcibly molded to what would've been the mid- Right when I was a kid growing up (90s-00s). This is because of Fox News. And then social media propagandists have tried ripping it to the extreme right, aka alt-right.
I imagine a lot of what younger people think of as left/liberal was very much a moderate view point just a generation ago.
So when you move to a new medium not propagandized yet (or at least a new venue like Lemmy) you might find that organic discourse is a lot more sane, tempered, and moderate.