I am using iPadOS 15.7 and I use VirtualBOX with the extensions which allows me to connect to the virtual machines via RDP; and for the last few months, I have noticed I cannot use any viral machine that requires me to use the keyboard, which is basically any virtual machine. For example I have a OpenSUSE LEAP virtual machine which I can use the keyboard to enter my password and other things using the RDP client on my Mac but I cannot on the iPad. I have even tried using the virtual keyboard and it seems the only key that get's sent to the virtual machine is the enter key and that is intermittent.
