Hello @Elmendorf , I have checked your store, and it seems like an app is preventing the checkout button, or you may have a script that overrides the add to cart function.
Can you please confirm it you added some code into your theme or which app you lastly added.
I highly recommend to switch to any other theme with simple layout just to keep your sales going on, maybe you have a draft theme with some features in the past. We can adjust that them until we fix this.
Regards,
Osama Farooqi