I am developing an Unlocked package that contains a simple application (a console application that contains two custom tables (Objects) used for configuring the core functionality of my package).
I was able to create a custom icon (Logo) for my app in my development org in the following way:

1. create a public document fiolder
2. upload, into that folder, my .png 'document'
3. replace the default salesforce cloud with my custom icon in the Custom App Detail page. 

After which I used the Org Browser to retrieve the modified / added metadata items:

The XXXApp.app-meta.xml now has an entry

<logo>XXX_App_Resource/XXX_App_Icon</logo>

XXX_App_Icon
XXX_App_Icon.document-meta.xml

When trying to install the package the system complains:

ERROR running force:package:install:  Installation errors: 
1) (XXX_App_Resource/XXX_App_Icon.png) Cannot find folder:XXX_App_Resource, Details: XXX_App_Resource/XXX_App_Icon.png: Cannot find folder:XXX_App_Resource

Have I overlooked something, or Is there an other way of achieving what I intend to do? 
Thanks in advance for any helpful hints.

here is the SOQL query and result for the folder 

[SELECT DeveloperName, AccessType, IsReadonly FROM Folder WHERE DeveloperName = 'XXX_App_Resource']

DEVELOPERNAME     ACCESSTYPE  ISREADONLY
────────────────  ──────────  ──────────
XXX_App_Resource  Public      true

and for the .png: 

[SELECT DeveloperName, BodyLength, ContentType, IsInternalUseOnly, IsPublic FROM Document WHERE Folder.DeveloperName = 'XXX_App_Resource']

DEVELOPERNAME  BODYLENGTH  CONTENTTYPE  ISINTERNALUSEONLY  ISPUBLIC
─────────────  ──────────  ───────────  ─────────────────  ────────
XXX_App_Icon   2030        image/png                       true