I have exactly the same problem with my A52s. Bold fonts do not apply to Whatsapp. Some fonts works but most of them are not. I factory reseted my device after the Android 13 and UI 5.0 update and reinstalled my apps. Even after the clean installation I have these problems and couldn't find a solution yet.
Hello Andrew, at that section of Whatsapp there is only font size adjustment is available as you know. Bold font setting is only available at phones Settings section. If you select bold font, it applies to all applications. In current situation, only exception is Whatsapp. This is the problem.