I suggest instead using `CHR$(13)` because that's what it required on Win32 API. This should work with Zenity on Linux. I should check if it could work on Yad as well because more systems (EndeavourOS, MX Linux) are using that instead.
On Linux the "tinyfiledialogs" functionality of QB64 might control what is the size of the `_MESSAGEBOX` which could interfere with your intentions displaying a message. The only alternative, however, is to call the dialog-making tool directly. With Zenity provide `--width=xxx` option to set the width of the message box.
The dialog-maker should be responsible for keeping the dialog centered on the screen if it's possible. But it could depend on the desktop and/or window system settings. For example on XFCE desktop there is a threshold for how large a dialog has to be so it could be considered for centering. Otherwise it pretty much could place the dialog in one corner of the screen which is annoying. This is almost not thought of on KDE (which Neon has and you say you use it).
On Linux the "tinyfiledialogs" functionality of QB64 might control what is the size of the `_MESSAGEBOX` which could interfere with your intentions displaying a message. The only alternative, however, is to call the dialog-making tool directly. With Zenity provide `--width=xxx` option to set the width of the message box.
The dialog-maker should be responsible for keeping the dialog centered on the screen if it's possible. But it could depend on the desktop and/or window system settings. For example on XFCE desktop there is a threshold for how large a dialog has to be so it could be considered for centering. Otherwise it pretty much could place the dialog in one corner of the screen which is annoying. This is almost not thought of on KDE (which Neon has and you say you use it).