"Cash for keys" is a payment to the owner or tenant to vacate the property. It doesn't matter if it is required by statute such as the Ellis Act or some other reason. The substance is that it is payment for a a personal expense (moving) and is not deductible because the move isn't employment related.
Your situation is unique and I doubt that you will find a specific mention of it on the IRS website (it doesn't include every possible situation.) However, here is one site (http://www.brickunderground.com/blog/2013/03/how_to_negotiate_a_buyout_by_your_landlord) that mentions it. Note the site's point 12:
"The tax consequences of a buyout. Payments for
surrendering a lease are taxable at ordinary income tax rates. It may
be possible to structure a buyout to reduce the tax consequences."
Here's another (https://thebolditalic.com/how-to-negotiate-a-buyout-from-a-landlord-the-bold-italic-san-francisco-9e...) that comes to the same conclusion, noting .“It will be taxed at your marginal tax rate, which is your highest tax rate.”
If the payment is very substantial, you might consider approaching a local tax consultant familiar with the area of buyouts, but I suspect they will come to the same conclusion.
