Questions about download manager free

Hello, I am a newbie in WordPress (and not a coder) and when in need of a download manager, this plugin came out as one of the best (if not “the” best) available.
I have also installed the Gutenberg blocks to easily include WPDM inside contents.
Unfortunately something fails to work, so please let me post here some questions.

1) If I enter the shortcode [wpdm_tree] nothing shows up on the page. I just get exactly [wpdm_tree] written as text. What can be wrong?
If I enter other WPDM shortcodes, they work just fine.

2) I tried to use the Gutenberg block named “Categories” and then I was invited to select the categories from the sidebar, but once chosen, a message appears (sorry I don’t know the exact translation) “An error occurred during the block loading. A critical error occurred to you website.” plus a reference to WordPress debugging. Is there maybe one or more common cause for this error?

3) I love the categories page included in the Directory Add-on so I would like to get it as it is exactly what I need for my website, but I am not sure if this Add-on is available for purchase only for the PRO version of WPDM, or it can be purchased and used also for the free version of the plugin.
In case I can purchase it, I am also a bit concerned about if it could work, considering the above issues 1 and 2.

The plugin version 3.0.97, WP version is 5.4.2.
Many thanks for any advise!