Hi @morphiazz,
Yes, you can do this with a small change to the HTML template of your Cookie Banner. I have already made the change in the template, you can override your current HTML template with this adapted version by following the steps provided below.
– Upload the “banner.php” file (attached below) to the folder /wp-content/mu-plugins/
banner.php (to override the current HTML template)
– Upload the “cookiebanner.php” file (attached below) to the folder /wp-content/mu-plugins/cookiebanner/
cookiebanner.php (the new template with Functional category opened by default)
After which your MU Plugins folder should appear like in the below screenshot:

Hope it helps!
Kind regards,
Jarno
Please note, that the above solution is needed to also expand the description of the functional category, as in your screenshot.
If you only need to show all categories by default, you can select this option in the cookie banner settings, by choosing for “categories” as option “accept-deny-save preferences”