Beau and the media coverage, and to a degree even the courts, are kind of missing the main point, which is that presidential immunity only covers acts performed as part of official duties. And that the courts get to decide what acts are and are not part of the official duties. It is logically impossible for inciting insurrection or assassinating political rivals to be part of the president's official duties.
But I almost hope that the court sides with Trump's team on this, because then all Biden has to do is whack a couple dozen senators to become unimpeachable, and then he can have Trump killed at leisure.