How to make ip route permanent

Q&A
1

we add a route to clearlinux server and it works fine. see route below.
ip route add 1.1.1.1/24 via 2.2.2.1 dev ens001
we want to make it permanent. what is the right way to do it.
network is managed by system.networkd

2

You can create .network files under /etc/systemd/network/*.network for systemd-networkd to configure.

Have a look at the Route section of the systemd.network man page.