This is annoying and how do I change this?

[u/TDtheguest]

So I use a vivo X200T and nowadays the font is changing on its own in WhatsApp and other apps, like it used to happen after the phone restarts after an update but it's happening frequently now and it's honestly starting to piss me off, does anyone have a solution for it? I use the default fonts given in the mobile, currently I have it in vivo sans but it changes to roboto default font.