To add a little more color... Magnus, in recent years, has been expressing his dislike for chess under classical time controls, seeing it as a battle of prep vs prep at the SuperGM level rather than skill vs skill. He doesn't seem to be enthusiastic about doing that prep anymore, and that seems to have been a factor in his decision to no longer fight for the WC title.

No, he retired from the championship circuit last year which is why Ding was champion in the first place.

He had concerns over the format and FIDE was unwilling to make changes.

We're in a bit of a weird spot in chess right now because Magnus is still the consensus best player even though he's not the official champion.

No, he did not compete in the last one either.

I suspect, the results would have been different if he had.