Yes, good to review history of the presidential order of succession.

https://en.m.wikipedia.org/wiki/United_States_presidential_line_of_succession

Also important to note, if there is a double vacancy (POTUS and VP gone) then the next down doesn't become President, but merely ACTS as president. This was a big issue with His Ascendancy John Tyler making himself President, even though originally under the Constitution, the text did not explicitly state that VP would automatically become president. This was settled via the 25th Amendment. But the 25th didn't settle what happens after VP, if double vacancy, leaving it to Congress to pass statutory law to deal with it. And at least to that end, it is settled as to who shall ACT but not become president. The current 1947 act is wrong about Speaker and Pro Tempore, which are constitutionally ineligible, so it would go next to Sec of State.

This all falls into my theory that we've had a shadow Acting president since Jan 2021, and possibly earlier. Regardless of what has been shown publicly (Trump still signing EOs and pardoning, etc up until Jan 20th), I believe he 25th'd himself, and possibly Pence 25th'd himself. Next in line, legally? Sec of State Pompeo. If there was no legal POTUS elect as of Jan 20, 2021 (which I argue there wasn't, Biden was not lawfully elected, the matter was still in unsettled dispute), then according to statutory law, the acting POTUS continues to act as such until a POTUS elect has qualified. So I think that this whole time, that's been Kansas.

But my mind wanders sooooo... take it with a grain of salt.