In Windows, I would have expected this from some zoom in feature for vision impaired person, or from changing system font size or similar.
Can you get to the drop down lists at the top of GCS? I am not running the Windows version, but commands may be similar.
Window -> FullScreen
may help (or for me, Ctrl-Shft-F11)
If it is a LibrePilot thing that I am unaware of, then running the gcs with a -reset option one time might clear it.
Finally, rebooting Windows may help, or uninstalling / reinstalling LibrePilot.