There is no stated IRS instruction/information regarding cold wallets. It is strongly recommended that account holders set up exchange accounts on a platform that enables sign up through entity signup, stores crypto in the centralized exchange account’s hot/cold storage, and allows submitting a W9 form.
If preferred, storing your IRA’s crypto in a cold wallet is fine as long as it is held by a custodian or a bank deposit safe registered under the IRA. Holding on to a form of cold wallet hardware personally – or not through a custodian – may be considered a prohibited action and creates risk for unwanted fees/penalties.