Tranmit any comination of modifyer keys, not just Ctrl+Alt+Del.

I have a client running Server 2019 in a VM. The backup software they use has a hidden CLI built into it that can only be accessed by using Ctrl+Shift+C. I am unable to enter that key combination on the remote machine. I tried enabling sticky keys but that feature doesn't apply to the onscreen keyboard. I also tried to remote into the server hosting the VM and ran into the same issue. Using that key combination only registered on the host, not the VM. At this point I have no ability to enter the CLI to perform the required procedure. I, of course, filed a complaint with the maker of the backup software, but it occurred to me that this feature really should be added to Control. I thought it might take the form of a button that captures all local keystrokes and transmits them to the client until the feature is turned off. Those of you that are Linux users and have used Remmina will be very familiar with this feature.