I have a question for this: "file 2553 (to change the tax regime to disregarded entity) and file 1040 schedule c"

Was this S Corp really in business or not? If there was no intent to act as an S Corp, or as an employee of that entity, and all documented work (business performed) is between customers and your taxpayer as an individual, perhaps there is no S Corp activity at all that year. You can form a corporation and not "switch" to it; perhaps it was for a different business purpose entirely.

What you cannot do is pretend to be both a corporate entity and an individual entity at the same time for the same work. And you don't get to pick which of the requirements you like, and not comply with those you don't like.

So, you can't have met S Corp requirements if there was no payroll and you don't intend to do payroll. If there are not business contracts using the FEIN, nor any employment processing, no banking, etc, then perhaps the S Corp is still an empty shell waiting for the Sole Properietorship to transfer assets and rights to be in business, to the S Corp, or for someone to start working for the S Corp.

We don't know all the details. That's your due diligence.

Not wanting to do what should be done is no reason to try something not provided for. Your own entity doesn't prepare and issue a 1099-NEC or -MISC for the labor you did for that entity. You are not a subcontractor expense to your own business entity.