Re the “debt ceiling”, there isn’t any. Every constitutional lawyer knows that. Section 4 of the 14th amendment makes explicit what was always (OK, Nino) the original understanding of the framers: “The validity of the public debt of United States, authorized by law… shall not be questioned.”
In fact, one of the principal reasons for the constitution, in the first place, was the need to have a central government capable of taking debt, because the States had taken on debt and had no ability to either pay or refinance.
So, I assume that Biden will never let the country default. He has a constitutional duty to make certain that never happens. If we should actually get close to that, I assume he will speak to the nation, teaching the constitution to the chattering class, and sign a memorandum on TV directing the Treasury Secretary to continue regular operations in selling and paying Treasury notes.