The line of succession goes past the Speaker, then to the Senate pro tempore (Patrick Leahy), then to the eligible cabinet members (a frightening thought, considering who’s in his cabinet)
Line of succession within the cabinet per WH.gov site:
VP Kamala Harris
Sec of State Antony Blinken
Sec of The Treas Dr. Janet Yellen
Sec of Def General Lloyd Austin
AG Merrick Garl &
Sec of the Int Deb Haaland
Sec of Agric Tom Vilsack
Sec of Commerce Gina Raimondo
Sec of Labor Marty Walsh
Sec of HHS Xavier Becerra
Sec of HUD Marcia Fudge
Sec of Transp Pete Buttigieg
Sec of Energy Jennifer Granholm
Sec of Educ Dr. Miguel Cardona
Sec of VA Denis Mcdonough
Sec of Homeland Sec Alejandro Mayorkas
Admin of EPA Michael Regan
Dir-National Intel Avril Haines
US Trade Rep Katherine Tai
US Amb to the UN Linda Thomas-Greenfield
Chair-Council Of Econ Advisers Dr. Cecilia Rouse
Admin-SBA Isabel Guzman
Dir-Office of Mgmt & Budget Shalanda Young
Chief of Staff Ron Klain
He’d be ineligible. It states it very clearly in the last sentence of the amendment. See post 16.