Any bolded Noto Serif text turns bold as well as italic.
This applies to new and existing documents.
Safe mode does not change this behavior, neither did repairing my installation of libre office.
EDIT:
I use Windows 10, LO version 24.8.2.1 (X86_64).
The Noto fonts came with the software. I did not install them on my own. Noto Serif Bold and Noto Serif Italic are both available. Noto Serif Bold displays as it should, but bolding the normal Noto Serif yields Bold+Italic.