Odoo has no minimum selling quantity feature.

The closest you can get without customization, for a random assortment of 6-item groups (i.e. 'My retailers can mix and match products (ie: 4 vanilla and 2 mocha), as long as there are 6') is by using Combo-type Products. The 'or more in total' part could be handled with automated actions checking on write, whether a certain quantity threshold is reached or not and displaying a message accordingly. This involves advanced Studio and View customization as well however.

The UI for adding such a Combo to a Sales Order would look similar to this:

The resulting Sales Orders would look like this:

The setup of this approach would allow you to sell a 6-pack with random (allowed) items. It would however not allow you to freely just add multiple additional items to that combo. This then would need to be separate lines in your Sales Order, or, an additional Combo with possibly different selections.

The Product configuration for this would be like this: 
A Product of type Combo with as many Combo Choices as items are allowed in the pack.

Each Combo Choice on the other hand would look like this:
A Choice of Product 1, Product 2, ... with 1 free quantity (as the price is given by the 'parent' Combo Product) - you could however modify the price by setting an Extra Price in addition.

An alternative approach could be the use of Bill of Materials (from the Manufacturing App) - but, this seems a bit of a stretch.

Another alternative approach could be to use a Pricelist for setting up a price for a Minimum Quantity of 6 on a product to cover for extra cost individual item handling would otherwise require.

You can find further details on Combo Products for example here: https://www.odoo.com/documentation/18.0/applications/sales/point_of_sale/combos.html
Above screens are created with a demo/playground instance of https://demo.odoo.com which you can use as well to test the functionality.