Creating Parts - 'Ok' is obscured by Taskbar in Windows 11

Click at the top of that Parts dialog window (in the title bar) and drag the entire window down a few inches. Then move the mouse cursor to the window's top edge (the cursor changes shape) click and drag the top edge down. This will make the Parts dialog window smaller. Drag the title bar of the (now smaller) window back up until you see the 'OK' at the bottom.

Alternatively, you can try right clicking on the taskbar and use taskbar settings to move or hide the taskbar.

Most likely your OS is scaling everything to be too big, probably because it thinks MuseScore isn't smart enough to scale itself correctly for your display. But MsueScore is perfectly capable ot doing so itself, and now your getting everything scaled twice, making it too big.

To fix, go to C:/Program Files/MuseScore3/bin (or wherever MuseScore is installed on your system), right-click the ".exe" file, Properties, Compatibility, and set the high DPI option to something other than whatever MIcrosoft thought would be most appropriate. Each system is different, but usually "System" or "System (enhanced)" works better.