Spellcheck is a browser-based feature and not the responsibility of websites to implement. (There is a spellcheck HTML attribute for input fields, but that doesn't take priority over people's browser settings.)
If you don't see spellchecking here, then you should check your browser settings to make sure it's enabled. Spellcheck may not be supporter by your browser to begin with. It's working for me on Firefox 91.
In general, we can't do anything about people's bad writing except encourage them to improve it (and fix it ourselves when that doesn't work).