Same.
User Interface: Menu Scale -> Legacy seems to fix this (mentioned above) but for those on larger screens, it might make the chat window be excessively large (you lose Custom scaling plus a lot of UI elements default to certain sizes, i.e. some will appear too large / too smol, depending on your customisations
*If you don't want messages in your chat window to pop up, make a "private tab", i.e. just right-click on someone in the chat window & click Talk - you're now in a private tab with that tenno and unless they send you a message... no more pop-ups