Before the Tax Cuts and Jobs Act, you could claim a personal exemption both for yourself and an NRA spouse who had no US source income when married filing separately. But to do so, obtention of an ITIN was required for the NRA spouse. As these personal exemptions have been eliminated (at least for tax years 2018-2025), there's currently no reason for married filing separately filers to obtain an ITIN for their NRA spouse.
Your situation is different, though, if you're choosing the married filing jointly status to file a federal return, in which case your spouse will need either an SSN or an ITIN (and be required to report worldwide income).
