I am amused that anyone other than a small child still believes this. The 9th and 10th have been phantoms for longer than you have been alive and are of absolutely no consequence whatsoever.
Oh yeah, there is no 'if' there buddy. Biden won and will be able to enforce any public health measures available to him via executive order starting January 20th.
Sure he can.
The exact parameters of any such mandate and its manner of enforcement is circumscribed, but that doesn't mean there is no legally-enforceable federal mask mandate. A direct federal individual mask mandate, with direct personal liability for violations, is least likely to be Constitutional.
A federal mandate that states adopt, enforce, and demonstrate adequate compliance with such a mandate, with failure resulting in additional restrictions on interstate travel and trade, is certainly not only within the power of the federal government under the Commerce Clause, but also the executive branch under the Public Health Services Act and other laws relating to federal commerce-related responses relating to public safety.
The thing that is lost on the national vs state debate is that the presidents role in a our state powered republic is mostly a sales job. Selling culture, building confidence, recruiting domestic and abroad. Having a new culture changes things whether you agree with the change or not. It's not a political statement, it's how the country works.