Prerequisite: Virtual Keyboard is activated. Virtual Keyboard doesn't pops up upon: 1. Clicking on 'Open File...', 'Open Directory...' and other windows with text input fields in VLC player. 2. Choosing 'Rename' in right click menu for any file/folder in Dolphin and selecting whole file/folder name text by clicking and dragging. Detailed explanation: let's say we have a file with name - 'neon.txt'. After right clicking on this file and choosing 'Rename' - we can just click in any place of name editing box and Virtual Keyboard will appear. Also we can click and drag cursor to select some part of file name in editing box - 'neo' part for example - and Virtual Keyboard will appear. But if you select 'neon.txt' whole file name in editing box - Virtual Keyboard will not appear.
Virtual Keyboard is only available if the applications support it. Your case 1 is due to VLC not using Wayland at all. Case 2 is a bug in dolphin. You have to report to Dolphin. I'm setting to INVALID as these are different bugs in different applications.