It was included as part of the American Rescue Plan passed in March 2021. The IRS can't unilaterally change federal law.

Clutter's Last Stand was a book if you can find a copy. Or maybe you have one under box #119.

Take the worst 10% of it and put it to the road with a donation box.

Look for bulk buyers on Craigslist wanted section.

America is awash in everything you can name. Sadly.

...while the wealthy and corporations are the biggest beneficiaries of tax loopholes and laws.

Screw the little guy selling off flea market stuff, or someone unloading grandma's collectibles.

It's really something awful.

Research each item and estimate cost plus sales tax. Any other expenses also count. Just inventory everything and make list on paper or a spreadsheet. Actually you just need to estimate year and know where to find digital catalogs like Sears, JC Pennies, Montgomery Ward use any of those after you sell something. It will only matter if you break $600 somewhere. You can put the stuff on a Schedule C, where you can take business expenses off the top before and normal income deductions.
Not accounting advice, just ideas to direct your research. Use DuckDuckGo to look for current advice about selling personal items bought years ago. If your reselling stuff it will be tougher.