It would be political suicide even to try for the Cabinet members and KH. They won't want to risk that. And it doesn't really solve "the problem", which is the nomination.
Now, maybe if Joe has more really bad days in public, they might be forced to attempt it, but it would have to be several really bad public days. The story to date is "Everything is fine here."
There would first be multiple high level efforts to get him to retire and resign quietly.
Since it has been brought up repeatedly, the 25th Amendment has four Sections:
Section 1 clarifies that the VP takes over in the event of the death, resignation, or removal of the President.
Section 2 lays out the procedure for filling a vacancy in the office of VP. The procedure is that POTUS nominates and BOTH Houses of Congress confirm by simple majority. IIRC, before the 25th Amendment the Senate alone filled vacancies in the office of VP. Gerald Ford became President when Nixon resigned. He had previously become VP under this section.
Section 3 lays out a voluntary procedure for temporarily transferring power to VP. This section has been invoked multiple times by Presidents starting with Bush II for things such as surgeries requiring general anesthesia.
Section 4 is the procedure for an involuntary transfer of Presidential power but note that this section transfers the powers, NOT the office. Ie, if it were invoked Harris would become "Acting President", NOT President. That may seem semantic and in a way it is but it matters because the invoking Section 4 would NOT create a vacancy in the office of VP. Biden would continue to be the President and Harris would continue to be VP, while acting as President.
Here is the text of Section 4:
Section 4
Whenever the Vice President and a majority of either the principal officers of the executive departments or of such other body as Congress may by law provide, transmit to the President pro tempore of the Senate and the Speaker of the House of Representatives their written declaration that the President is unable to discharge the powers and duties of his office, the Vice President shall immediately assume the powers and duties of the office as Acting President.
Thereafter, when the President transmits to the President pro tempore of the Senate and the Speaker of the House of Representatives his written declaration that no inability exists, he shall resume the powers and duties of his office unless the Vice President and a majority of either the principal officers of the executive department or of such other body as Congress may by law provide, transmit within four days to the President pro tempore of the Senate and the Speaker of the House of Representatives their written declaration that the President is unable to discharge the powers and duties of his office. Thereupon Congress shall decide the issue, assembling within forty-eight hours for that purpose if not in session. If the Congress, within twenty-one days after receipt of the latter written declaration, or, if Congress is not in session, within twenty-one days after Congress is required to assemble, determines by two-thirds vote of both Houses that the President is unable to discharge the powers and duties of his office, the Vice President shall continue to discharge the same as Acting President; otherwise, the President shall resume the powers and duties of his office.