With a similar scenario, we can have 4 presidents in 2025:
January 1, 2025 - January 2, 2025: Biden is president until he dies from a stroke
January 2, 2025: - Trump inauguration: Harris is president until she hands over the presidency to Trump
Trump inauguration - Trump heart attack: Trump is president until he dies from a heart attack
post-Trump heart attack: The VP becomes president