How do I embed a 2nd level menu block?
Not quite sure, whether I got you right. Here's my guess:
Depending on which theme you use, it may be that it is not a problem with the menu template. In my case, the (main) menu was configured to show only one level in the block settings.

I found out by chance, here is how to change it:


Go to https://&lt;yourdrupalpage&gt;/admin/structure/block
on the respective menu block item (e.g. main menu) click configure
adjust the number of visible menu levels to your needs


that should to the trick