State law here adds to federal law; it does not replace it. Every city, county, school district and special district in Washington is bound by the federal Title II web rule, 28 CFR 35.200, which requires WCAG 2.1 Level AA on web content and mobile apps: from April 26, 2027 for public entities of 50,000 people or more, and from April 26, 2028 for smaller entities and special districts. State agencies are bound by the same rule at the earlier date.
Private businesses open to the public answer to ADA Title III. A private plaintiff can sue for an injunction and ask for attorney's fees; the Department of Justice can sue for damages and civil penalties. No federal regulation names a web standard for businesses, so audits use WCAG 2.1 or 2.2 Level AA as the working benchmark.