Using 25th Amendment Article II, Section 1 and 2, if Biden resigns, dies or removed from office:
Section 1. Kamala Harris becomes Acting President.
Section 2. Harris nominates a new Vice President.(Pelosi?)
Both Houses of Congress confirms with majority vote.

👉If President & Vice President simultaneously are vacant
power and duties of presidency pass to the current speaker of
the House of Represenntatives...Nancy Pelosi.👈