After changing the screen resolution from Full HD (1920 x 1080) to 4K (3840 x 2160), the Media Portal Titan skin's text got way too small.
To resolve the issue, all I had to do was clear the skin's cache. To do that, navigate to C:\ProgramData\Team MediaPortal\MediaPortal\Cache\ and delete a folder with your skin's name (in my case Titan).
After restarting MediaPortal, everything is looking fine again.
Windows 10 Pro (22H2)