FWIW, everything works fine in my application if I use Qt WebKit 5.212.0 Alpha 3.
However, I have also built both Alpha 3 and Alpha 4 on their own, and checked https://lemonde.fr/ with MiniBrowser and QtTestBrowser and:
MiniBrowser crashes uploading https://lemonde.fr/ and this with both Alpha 3 and Alpha 4;
QtTestBrowser loads https://lemonde.fr/ fine (or so it seems), but will eventually crash when loading another page (after clicking on one of the links) on that website. This, using both Alpha 3 and Alpha 4.
So, I have no idea why https://lemonde.fr/ works fine in my application using Alpha 3, but it does...!?