@bertrand66 For pro or commercial product support please contact the developer directly on their site. This includes any pre-sales topics as well. As the developer is aware, commercial products are not supported in these forums. I am sure they will have no problem supporting you there
The top-bar plugin os always just 1 form. But it is possible to add a tag or interest group via custom code. That code could be adapted to set a tag orr interest group based on what category a user is viewing.
https://github.com/ibericode/mailchimp-for-wordpress/blob/master/sample-code-snippets/add-ons/top-bar/add-subscriber-tag.php
https://github.com/ibericode/mailchimp-for-wordpress/blob/master/sample-code-snippets/add-ons/top-bar/add-to-interest-groups.php
Note that a post can have multiple categories, and some pages don’t have a category assigned to them (eg the homepage or a contact page). So you would have to write some extra code to handle all those situations.
Using the Premium add-on you can make multiple forms, one for each category, but those forms are not shown in the Topbar, they are added via a shortcode or a widget, for example in a sidebar of footer widget area. There is another plugin that you can use to show “conditional widgets” to help you show a different form per category.
Hope that helps. If you have any questions, please let me know!