8 – CSS and JS 404 on the administrator site only – New installation

This is a new version of the server …

me@server:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.3 LTS
Release:    18.04
Codename:   bionic

Apache …

me@server:~$ apache2 -v
Server version: Apache/2.4.29 (Ubuntu)
Server built:   2019-09-16T12:58:48

I downloaded the Drupal 8.7.8 tar.gz and installed with the help of Standard installation profile in an Apache VirtualHost. The visitor portion of the site displays and works as expected, but the admin part has problems. The main page, / admin, displays stylish. However, by clicking on the different links, Content, Structure, Appearance, etc., you get a page without style. The Inspect Network tab indicates …

http://my.server/admin/sites/default/files/css/css_.css?0
...
http://my.server/admin/core/assets/vendor/modernizr/modernizr.min.js?v=3.3.1
http://my.server/admin/sites/default/files/js/js_.js
...

Still under Inspect on the Network tab, CSS files display a "(cancelled)"and the JS files are all 404.

Maybe I have a problem with rewriting URLs. When installing in the "Requirements Verification", I received the warning regarding clean URLs – the server is capable but is not enabled. Good, mod_rewrite is activated and I have the following items in my VirtualHost config …

RewriteEngine on
RewriteCond %{DOCUMENT_ROOT}%{REQUEST_FILENAME} !-f
RewriteCond %{DOCUMENT_ROOT}%{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /index.php?q=$1 (L,QSA)

With adjustment RewriteEngine off the visitor site only partially works. For example, the contact form is 404 while the search is working but does not contain CSS code.

All other prerequisites are passed.

I removed the entire Drupal file system and threw away the database. Another new installation gives the same results. Also suggesting that this is an Apache configuration issue.

Your time and your help to solve this are appreciated, thank you.