Hello, hhow can i add in toolbar a custom bbcode
I want to add [download] [/download] with specific image and href to download link.

As per:

BBCode was deprecated in the IPB platform back in like 2020.

It is not possible to add custom bbcode, and parsing of bbcode itself is officially depreciated.  In fact, if you enable support for parsing it gives the following warning:

  Quote

BBCode is a legacy markup language that was originally designed to allow users to submit rich content prior to the advancement of WYSIWYG editors. BBCode support is deprecated and may be removed in a future release, and we recommend leaving this option disabled for greater performance and reliability if your community does not rely on BBCode parsing to format posts.

 

What you should actually do instead of trying to replicate old BBCode, would be to use a button for this purpose. You can read how to do this here