Correct. See https://constitutioncenter.org/blog/understanding-the-constitutions-25th-amendment for a good writeup.

However - this is not an easy or fast process. When is the last time 2/3 of both the house and senate agreed on anything?

Here is the important part from the article:

The 25th Amendment sets a high bar to use Section 4. Once the vice president and either the cabinet or a disability review panel agree to invoke the amendment, the vice president is allowed immediately to “assume the powers and duties of the office as Acting President.” The president can then notify Congress that “no inability exists” and he “shall resume the powers and duties of his office.” In that case, he can resume the powers of office unless the vice president and the cabinet or body formed by Congress jointly object.

If not in session, Congress is required to convene within 48 hours once the 25th Amendment is invoked. When in session, Congress has 21 days to settle the question if the president notifies Congress in writing that no inability exists. The vice president and the cabinet or disability body has four days to file an objection to the president’s declaration within that 21-day time frame. If no objection is filed, the president resumes his duties.

If the president’s declaration is contested, two-thirds of the House and Senate must agree to allow the vice president to act as president until the president is considered able to serve, and the president can file another declaration about his ability to serve after Congress votes on the question.