Hi,
From what I can see the issue is linked to this message you have on each product details page:
"This item will be sold starting on 2106-02-07"
This indicates that the system believes you have something entered in the "Available from" setting of the product and that the date entered is in the future.
So I would recommend to check on that.
And if you want, you can change that value for all your products in one go with a mass action via the menu System>Mass actions.
There, you can use an action "update the values" on the product_sale_start column with the "string" mode and the value empty. Once you process the mass action, it will remove that date from your products and you should hopefully see the add to cart buttons.