Hey there Adobe employee, you marked your own bad advice as the "Correct answer" but you linked to a thread that's not only moralistic about NEVER EVER EVER EVER deleting RAW files, but admits that there is absolutely no way to do this. Adobe has failed at offering the simple feature.
The link to the Lightroom Queen forum is a very old discussion about what is now called Lightroom Classic. It deals with a situation where the photographer shot raw+jpeg. This question seems to be about keeping a processed jpeg made from an edited raw file, and deleting the raw original. That is not the same thing at all, so I 'undid' the correct answer selection.
Doing that is indeed not something I would advise. It's like throwing away a negative after you've made a print. It's much better to keep the original, and only export a jpeg if and when you need one. Each time you can export a jpeg that is suited for that particular purpose, so sometimes it may be quite large because you want to order a print, and another time it's small because you only want to send an email copy. That is the whole idea about Lightroom.
Because Lightroom is a non-destructive editor, it does not offer a standard feature to keep a jpeg and delete the raw file. That doesn't mean it can't be done, however. All you need to do is edit the raw file, export a jpeg from that edited raw file and import the jpeg into Lightroom. Then you can delete that raw file if you still think that is a good idea.