WCAG accessible basemaps are now available via ArcGIS Living Atlas as "enhanced contrast basemaps" for easier readability for those visually impaired.
Basemaps come in a light and dark version
The maps are available in both Web Mercator and WGS84. They can be opened directly from the Living Atlas website and can be added to your custom basemap gallery.
See Working with Enhanced Contrast Basemaps for more information, or view all enhanced contrast maps and layers by searching the ArcGIS Living Atlas website.