getcap and setcap are used to allow the Nginx version that’s bundled with Local to bind on ports 80 and 443.
You can either:
A. Install libcap2-bin using Apt (https://unix.stackexchange.com/a/455234 for more details)
B. Upgrade to Local 5.1 or newer and change the Router mode to localhost under Preferences » Advanced. This will disable the routing layer thus negating the need to bind on ports 80 and 443.
Note: at the time of writing Local 5.1 is still in beta so you will need to join the Local Beta program to get access.
In the meantime, I’ve added a note to look into adding libcap2-bin as a dependency in the .deb's we provide.