Pressing and holding for accents, tildes, and others does not work after software update.

After updating the software to the latest available version (10.15.2) I encountered a big problem: The Press and Hold function of both my keyboard and Touch Bar stopped working. I can no longer hold down a key and search for the necessary diacritical mark. It is extremely inconvenient to me, since I am actively typing in up to four different languages. I know there are other ways to get the character that you need, but they all happen to be extremely time consuming and not practical at all. All that happens when I hold down a key is I'll get the corresponding character repeated over and over again. I have looked everywhere for a solution to this problem, which led me to realise it is not uncommon and has been happening to random users after updating the OS for more than 5 years. I have tried every single one of the options presented to them by members of this community, as well as experts and members of various other forums (Terminal commands, rebooting, all possible combinations of 'Key Repeat' and 'Delay until Repeat' settings, having various active keyboards in contrasting languages, etc.). As one would expect by my asking, nothing has proven helpful. Could there be any other possible solution I might have overlooked?