Can you put up a screenshot of the problem please?
The signature space is to put the relevant details of your computer and version of your Magix software and operating system into, so we don't have to ask for too many further details. Look at some other people's signatures to see what I mean.
Try just double left clicking the black lettering twice in rapid succession with your mouse. If after that, if you see a tick on the screen, click that as well.
Alternatively when you finish typing your text in the box, don't forget to press 'Enter' on your keyboard.
Also, thank you for putting a bit more information in your signature.
. . . . Alternatively when you finish typing your text in the box, don't forget to press 'Enter' on your keyboard. . . . .
That does not work on my PC - it starts a new line in the text box.
The tick is the best way to finish text editing, deselecting the title object on the timeline also works but occasionally fails and results in what you are seeing.