I saw someone else complain about that - Shopping list deleted with one icon? - #3 by megapint - I guess I didn’t understand the use case. Yours makes sense.
You could (But I’ve not tried) have one card which displays the list and another which takes a text input and then adds that item to the list. And not actually use the shopping list card.
Actually I have the first one :
type: custom:mushroom-entity-card
entity: sensor.shopping_list
icon: fas:shopping-basket
name: ' '
card_mod:
style: |
ha-card
{
--chip-font-size: 0.8em;
--chip-height: 50px;
}