Ok. Finally found the bug. The bug is with Mobile-GUI, potentially with the combination of the Chat module.
When I recently added MongoDB to the game to make it MMORPG, I couldn't click Login/Create Account / Menu button / Action button, nor select the textboxes.
Upon removing the import mobileGui from '@rpgjs/mobile-gui', I could click the buttons. However, this does mean a lot of the in game texts / popup boxes are gone, along with the menu/action buttons.