Not OpenSource, but free, reliable and private, online right in your browser, it's a complete word processor, you can also edit Html, select webpages and paste it in the editor which conserve the original UI with all working links, Files and documets are stored locally in .htm, .pdf or .txt. Blazing fast and works also in mobile, even as PWA.

https://bluevelvet.ssuiteoffice.com/

(Part of the SSuite, it's a hobby project of two elictricians which make money with their workshop, not with these apps, no commercial interests, no ads, logs, tracking or othe crap, no account)