VPN network-manager-libreswan was never ported to Debian/Ubuntu. It changed its name from NetworkManager-openswan to NetworkManager-libreswan with version 1.2, but is still compatible with openswan.
If you need an IPsec IKEv2 with PSK VPN connection, I think the only solution is to build NetworkManager-libreswan from source code as NetworkManager-strongswan doesn't support PSK.
If you were trying to do an IPsec IKEv1 Xauth (Cisco-style) VPN connection which neither network-manager-l2tp nor network-manager-strongswan can do, you could try network-manager-vpnc which does Cisco-style IPsec IKEv1 Xauth VPN connections.
sudo apt install network-manager-l2tp-gnome
? wiki.archlinux.org/title/Openswan_L2TP/IPsec_VPN_client_setupapt show network-manager-l2tp
"with optional IPsec support." If I doapt search network-manager ikev2
I seenetwork-manager-strongswan
andstrongswan-nm
. You can look at the list of swan packages available at packages.ubuntu.com/…