Accessibility is for all user experiences, not just websites. WCAG is still a good resource for native apps even where some specifics do not 100% apply.
If Qwasm is referring to Quake, it absolutely should have, for example, legible color contrast and be usable if you are colorblind.
What else do you build on the web with a UI framework if not a website? If you're making a distinction between websites and webapps, it's equally important for both to be accessible and work as expected with a browser.
VSCode is a webapp [1], that is most often used wrapped in a shell that lets it act as a desktop app.
Even if you do consider it separate from webapps, it should still work with tab navigation and screen readers, which rendering to `<canvas>` doesn't allow for (at least without some very hacky workarounds).
Flutter faces a similar problem; to render cross-platform, they use a custom layer not standard to the system, and then try to emulate all the behaviors of a native app, which often feels broken and unnatural and is wasted work because the engineers are just rewriting and reshipping everything the platform already offers—at the cost of accessibility and general user experience.
Would you complain that Qwasm/Dwasm doesn't follow HTML standards of accessibility?