That's complicated. If it is theft, the answer is no, because theft losses are disallowed for 2018-2025 unless in connection with a declared disaster. If it is a non-business bad debt, it is a capital loss you can deduct against other capital gains.
https://www.irs.gov/taxtopics/tc453
https://turbotax.intuit.com/tax-tips/irs-tax-return/how-to-report-non-business-bad-debt-on-a-tax-ret...
https://www.grfcpa.com/resource/bad-debts-what-losses-can-you-deduct-and-when/
The problem is that the IRS can be skeptical of bad debt losses. There was a tax court case over forged paintings, that turned on whether it was theft (fraud) or just a bad investment, and the ruling was that for it to be theft, there must be a thief who benefits.
So you may need to look to see if this was a legitimate debt reduction company that went out of business, or if it was a scam all along. If it was a scam all along, the theft deduction is not allowed.
