Huh! The titlescreen? If it's working you should be able to click on the 'Start Game' button, or any of the small arrows to cycle through portraits / human/ cpu player. The top left of the cursor ( the light orange part ) is the click zone.
Hmm, maybe I recreated your problem. I tried dosbox-x and i couldn't move the mouse cursor, but left click was registering. To fix it, I clicked 'Main / Capture Mouse'. I guess dosbox-x doesn't automatically capture the mouse sometimes? Let me know if that fixes your problem