Custom Taxonomies will be specific to each site.
If you were to create your custom taxonomies as a plugin, you could activate this plugin in all sites and all of them will have the custom taxonomies. BUT, even then, the data that you enter into each of the taxonomies will be unique to each site.
There might be a way to share them across your multisite network since all of your sites could share the same database. For this I’d recommend reading this article which explains a little more about how taxonomies and terms are stored in the database, and a possible way for you to do this. Personally I haven’t tried this, but at the same time, I don’t think it would be recommended, at least for most cases.
https://buddydev.com/want-global-categories-tags-taxonomies-across-wordpress-multisite-network/
Hope this helps