Burned ubuntu-19.10-preinstalled-server-arm64+raspi3.img.xz. First boot on RaspberryPi 4 looked ok until it hung after
[ OK ] Reached target Cloud-init target.
Power cycled, and boot ended with
Ubuntu 19.10 ubuntu tty Ubuntu login: [ 23.431015] cloud-init… [...] cloud-init…
Then no response to keyboard input, in USB2 or 3 port. The same procedure worked fine (successful login, etc) on first boot with a RaspberryPi 3.