Hi,
Please check if the package is included:
nvidia@xavier32G:~$ apt list | grep deepstream
WARNING: apt does not have a stable CLI interface. Use with caution in scripts.
deepstream-5.0/stable 5.0.1-1 arm64
deepstream-5.1/stable,now 5.1.0-1 arm64 [installed]
And then install it through sudo apt install.