No it is not true, BUT ...
it is not done in the standard way and has special requirements:
1. You must sell ALL your IRA assets (even if held at multiple custodians), so gains in one asset would then offset losses in others. You will need a net loss.
2. You can then deduct the net loss as a miscellaneous deduction subject to a 2% floor of AGI on Schedule A if you itemize.
These 2 requirements are usually so onerous that no one can use them. That is, you have to have a net loss loss for the sum of all your IRA assets of more than 2% of your AGI to do this. The same criteria can be used to tax-loss harvest a 529 plan which I have done.
It's all about short-term opportunistic rebalancing due to a short-term change in one's asset allocation, uh, I mean opportunistic rebalancing, uh I mean rebalancing, uh I mean market timing.