@elettrona You haven’t really indicated why the stuff you named, which claims to solve your problem, doesn’t. So it’s hard to suggest something that has a feature you want or doesn’t have a problem behaviour. “Go beyond Wordpress” isn’t much to go on.
“Manageable by spam filters” means what? It is more permissive by using a captcha, but offers a way to filter? I think Akismet is a service that will help there. But that’s not self hosted.
Accessibility in front and back end: front ends are often very customisable. So what is the accessibility gap on the front end now? Most software is terrible at accessibility. So what are your top complaints about the back end accessibility.
You might want to see what they are running at what https://degooglisons-internet.org/en/ offers as their replacement for Google Forms. They are an online service, but a lot (everything?) they offer online is open source you can self host if you want.
