Licensed attorney here, general info only and not advice for your specific situation. A few things to separate out, because people conflate them. First, severance: in most US jurisdictions there is no automatic legal entitlement to it. It generally has to come from a contract, an offer letter, a written policy, or sometimes an established practice. Read your documents for that.
Second, the layoff itself: most US employment is at-will, so eliminating a role, including replacing it with software, is usually lawful by itself. It becomes a problem when the real motive is something protected (age, disability, retaliation for protected activity, etc.) or when a larger mass layoff triggers advance-notice laws. Whether any notice law applies depends on headcount and how many were let go, so the facts matter.
Third, and this is where I'd focus: unpaid final wages, overtime, and any required PTO payout. Those are concrete and enforceable. I'd document hours and amounts and look at your state's wage agency. This is general information, not legal advice, and laws vary by state.