When manually specifying routes, OpenVPN allows special keywords "vpn_gateway", "net_gateway" and "remote_host" for the the remote vpn endpoint address, the pre-existing net gateway, and the remote client address. However, in the route configuration windows in the connection editor (IPv4-->Routes), only plain ip addresses are allowed. Please also allow these three keywords to be entered. Reproducible: Always Steps to Reproduce: see above Actual Results: see above Expected Results: see above
Unfortunately this doesn't seem to be possible to set through NetworkManager-OpenVPN plugin. The IPv4 tab is generic for all connection types so you should be looking for those options in OpenVPN configuration, however as I said, NM doesn't allow to specify those properties.