In this case it remains to add the missing HTML code using js code:

const loader = document.getElementById('wp-auth-check-form');

loader.insertAdjacentHTML('afterbegin', `
  <div class="spinner-border loading-icon" role="status"></div>
  <span class="loading-text">Loading...</span>
`);

You need to add it before loading MDB.

Thanks for the snippet, I could now locate (at least one place) of the conflict.

    <div id="wp-auth-check-wrap" class="hidden">
        <div id="wp-auth-check-bg"></div>
        <div id="wp-auth-check">
            <button type="button" class="wp-auth-check-close button-link">
                <span class="screen-reader-text">Dialog schließen</span>
            </button>
            <div id="wp-auth-check-form" class="loading" data-src="..."></div>
            <div class="wp-auth-fallback">
                <p>
                    <b class="wp-auth-fallback-expired" tabindex="0">Sitzung abgelaufen</b>
                </p>
                <p>
                    <a href="https://aviva-selection.local/wp-login.php" target="_blank">Bitte melde dich erneut an.</a>

                            Die Anmelde-Seite wird sich in einem neuen Tab öffnen. Nach dem Anmelden kannst du das Tab schließen und zu dieser Seite zurückkehren.
                </p>
            </div>
        </div>
    </div>

this Part of the WP Admin Page uses the class "loading". Unfortunately this part is related to the WP Admin core and I cannot change it.

Any Idea?

It is very possible that the error is causing incorrect code in your project. Check out this snippet: https://mdbootstrap.com/snippets/standard/grzegorz-bujanski/3549531#html-tab-view

I added a code that causes such an error, and underneath, the correct code commented out, for which this error does not occur.

Check if there is such an error in your project. The error with all.min.js should disappear after this fix. If it persists, please provide a screenshot of the exact error and what it refers to.

I'm sorry to not being enough precise, but I get the errors in safari this way.

The first error is from mdb.min.js: webpack://mdb/./src/js/pro/loading-management/index.js

The second error is from all.min.js: webpack://WYSIWYG/webpack/bootstrap

Safari just shows the link to the web pack source of mdb.min.js

I try to design an admin page for my plugin and reference to the mdb pro files I downloaded. The page is of course surrounded by the Wordpress admin.php which loads tons of styles and scripts which, I guess, interfere somewhere with MDB Pro.

In the Wordpress Frontend with DIVI Theme all works fine, but not in WP Admin The free Version works fine also, so the conflict must be in Pro.