Hi,
The field you marked on your screenshot is not a grouping category - it is Block name of the block opened in Block editor.
Looks like drawings you downloaded have multiple blocks inside them with the same names inside each "category" drawing. So you need to rename blocks inside drawings you downloaded from site before inserting them into your project file.
Otherwise, you will always run into a block name conflict and - if the block with the name you are trying to insert from external drawing already exists in your target drawing, it's definition (contents) will remain as it is in target file.
Can you attach here one of the drawings with blocks you downloaded from Minotti site?