LO's present spellcheck probably serves most people well. But for many who handle large documents it is not workable.

I often work on older classics, which can be written in British English or use passe wording. And then there are OCR errors to correct as well. What I expect to happen with spellcheck is that if I click "Correct All" instances of a misspelled word, it actually will do so.

And for shorter documents, it does. If you paste this into Writer:

misspellingxxx misspellingxxx misspellingxxx misspellingxxx misspellingxxx misspellingxxx misspellingxxx misspellingxxx misspellingxxx misspellingxxx misspellingxxx misspellingxxx misspellingxxx misspellingxxx misspellingxxx

and do a "correct all", the whole paragraph is immediately corrected. Perfect.

But if that paragraph is at the end of a long document, and you "correct all" one instance of "misspellingxxx" at the doc beginning, nothing happens to the last paragraph.

It gets worse. As you progress with spellcheck, other instances of "misspellingxxx" along the way will not have been changed. You will have to manually correct them. So the answer is not to let spellcheck advance to the end of the document to make all the Correct All changes. And that would be impossible anyway in one sitting with a multi-hundred page document.

I've tried many online spellchecks, and they also are not very good. Some don’t even have a Correct All function. Others have grammar check hardwired into it , something I'm not interested in.

Currently I am using spellcheck alongside Find and Replace, from which I can actually "correct all". But it is quite unwieldy.