Set site URI for drush uli without 'default'
I'm writing this up for posterity, since the Slack is relatively ephemeral. Here's the current method, following Providing custom environment variables to a container:

In e.g. .ddev/docker-compose.environment.yml put the following:

version: '3.6'

services:
  web:
    environment:
      - DRUSH_OPTIONS_URI=http://my.ddev.local


Then ddev rm and ddev start to prove to see it working. (This works for drush uli inside the container, after ddev ssh.)