I have an issue similar to the question Bold=Bold Italic, with the difference that I only see the issue with the font “Noto Serif”. I am running Libre Office Writer on Arch Linux. When I use the font viewer of my KDE desktop I can inspect the font and can see a different rendering of Bold and Bold Italic.
The font was installed with the normal noto font package
I don’t know whether there is really a problem with Libre Office or not though I can see the issue with Libre Office. Inkscape for example renders Bold correctly Bold and not also Italic.
I see this in all documents, whether I use an existing one or create a new one from scratch.
Do you have any ideas what I could further investigate?