Fortunately, with systemd-networkd + wpa_supplicant you could go without any of {netplan, ifupdown, NetworkManager} on both modern Ubuntu or modern Debian. As you may imagine, netplan is just a frontend generating ("rendering") configs for one of possible backends within {networkd, NetworkManager}. So you just copy /run/systemd/network/* into /etc/systemd/network/ , after which you may remove all netplan and related packages and go ahead with systemd-networkd only (which, unfortunately, is nailed to the core of modern Linuxes pretty firmly and not that easily detachable).
Fortunately, with systemd-networkd + wpa_supplicant you could go without any of {netplan, ifupdown, NetworkManager} on both modern Ubuntu or modern Debian. As you may imagine, netplan is just a frontend generating ("rendering") configs for one of possible backends within {networkd, NetworkManager}. So you just copy /run/systemd/ network/ * into /etc/systemd/ network/ , after which you may remove all netplan and related packages and go ahead with systemd-networkd only (which, unfortunately, is nailed to the core of modern Linuxes pretty firmly and not that easily detachable).