Comment 9 for bug 1867375

> Also is it planned to be included with simple updates or only in a future "Ubuntu 20.10" release?

this is fixed in the systemd version currently in the upload queue for Focal, so once that is accepted and assuming there are no regressions while it is tested in the -proposed pocket, this bug should be fixed for Focal when it is released to focal-updates. That will probably be in around 2 weeks, maybe earlier, but it also could take longer.

Once the fixed package is released, there will be a UseGateway option for networkd (in the [DHCPv4] section only - not in the deprecated/legacy [DHCP] section), but it also will default to the value of UseRoutes so you can just continue to set use-routes=false in netplan and it will work to disable both classless/static dhcp routes as well as the dhcp gateway route, just as it did in previous releases.

Setting UseRoutes=false and UseGateway=true, which seems uncommon but sometimes needed, is not currently possible with netplan, and would need an update to the netplan schema to add a 'use-gateway' option, which is why this bug is marked as affecting netplan as well as systemd.

If you want to test, you can try the build from this ppa:
https://launchpad.net/~ddstreet/+archive/ubuntu/systemd
please use that only for testing.