Accessibility on the Admin End of WP Form Plugins is really tough.

The challenge is creating an easy to use visual drag & drop interface, that most WP form plugins now use, while supporting keyboard and screen readers.

I think our best chance for accessibility for forms on the WP Admin (for creating at least basic contact forms) is the Gutenberg Form Block -https://github.com/WordPress/gutenberg/pull/44214.

The Gutenberg team focuses on accessibility & has the resources to tackle this complex task. Hopefully WordPress form plugin developers can follow this initiative.