root@Andromeda:~# nmcli con show "Wired connection 1" | grep -i routes
ipv4.routes:                            --

root@Andromeda:~# nmcli con modify "Wired connection 1" +ipv4.routes "188.88.88.88/23 172.16.2.1"
root@Andromeda:~# nmcli connection up "Wired connection 1"
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/8)
root@Andromeda:~# nmcli con show "Wired connection 1" | grep -i routes
ipv4.routes:                            { ip = 188.88.88.88/23, nh = 172.16.2.1 }

root@Andromeda:~# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         speedport-entry 0.0.0.0         UG    100    0        0 enp3s0
10.10.10.0      0.0.0.0         255.255.255.240 U     0      0        0 br-f8186d7831df
link-local      0.0.0.0         255.255.0.0     U     1000   0        0 enp3s0
172.17.0.0      0.0.0.0         255.255.0.0     U     0      0        0 docker0
192.168.1.0     0.0.0.0         255.255.255.0   U     100    0        0 enp3s0
root@Andromeda:~# ip route
default via 192.168.1.1 dev enp3s0 proto dhcp metric 100
10.10.10.0/28 dev br-f8186d7831df proto kernel scope link src 10.10.10.1 linkdown
169.254.0.0/16 dev enp3s0 scope link metric 1000
172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1 linkdown
192.168.1.0/24 dev enp3s0 proto kernel scope link src 192.168.1.6 metric 100