The free self-hosted version you can download from https://languagetool.org/download/ lacks all the premium rules (several thousand rules for English, German, French, Spanish and Dutch) and AI-based rules.[1]
My suspicion is the basic self-hosted version may no better then what you would already get in something like LibreOffice.
[1]: https://github.com/languagetool-org/languagetool/issues/6750
The free rules are pretty good IMO, I never used Premium and free was already on Grammarly’s level when I switched many years ago.
Safes effort with maintaining an installation and keeping the background process running. Plus, it also works when network connectivity drops.
https://github.com/Erikvl87/docker-languagetool/blob/master/...