How can i use special characters with Real VNC Viewer?

I use Real VNC Viewer on 2 Android devices. All my computers use Ubuntu 20.04 with TigerVNC-Server. I can't use special characters (@, /, ...) when i connect from android to the VNC-Server using Real VNC Viewer. Nothing happens when i type the character. I don't haven this problem when i connect from my Notebook (Ubuntu 20.04 with Remmina as VNC-Client). Here almost all characters are working.

Is this a limitation of VNC Viewer or a Server Problem?