adding custom devices to channel does not work

When following the instructions here:

https://documentation.bloomreach.com/library/concepts/template-composer/device-preview.html

I expect to be able to customise and add to a list of device previews for a given channel. This does not seem to work.

Reproduction:

1. Create a 13.0.0-1 archetype

2. add news via essentials

3. rebuild

4. Go to hst:myproject/hst:configurations/myproject/hst:workspace/hst:channel

5. add property hst:devices values ["custom1:100px", "custom2:200px", "custom3:300px", "custom4:400px"]

expected:

when opening the channel in the Channel Manager, I should see 4 custom device previews

observed:

the default device previews

no useful information spotted in logs