Hello again :)
That's very weird, you need to debug the Enter button to track which condition exactly is causing the issue:
Open the project → MainMenu scene → Username and loading saved data → Enter button and username rules → in the first event → remove all conditions, and leave these 2 conditions only (Left mouse button is pressed | Cursor is on EnterButton) → Try the game now → if it works, then start re adding the conditions you deleted 1 by 1 until the bug appear again, then let me know which condition is causing this issue.
Sure, i work as a freelancer game developer, if you need something, just hit me up on discord with all details 😉
Discord name: vegetato