I'm desperately trying to find a solution to how slow our *add to cart* is. If you watch the video below, it takes nearly 12 seconds for the site to add the item(s) and custom product options to the cart.
I have cleared all cache, used multiple devices, mobile, laptop, desktop, windows and mac, wifi and cellular, slow 200Mbps @ home, and our 1Gig fiber at work. Multiple browsers in normal and incognito modes. Nothing has an impact on the speed.
Keep always in mind others do not see what you see or know what you know. Always provide relevant context so others can understand, inspect or reproduce issues.
Make sure any links are publicly accessible by testing in an incognito window to see how another person would encounter it. Context such as: For theme problems always provide store url or preview urls, link directly to issue pages don't make others dig, exact demo urls, storefront password if any, theme name, example code, are any apps involved , etc . For browser problems browser name& version, operating system, etc.
Random troubleshooting guesswork,
Try in a fresh theme install, no apps.
If using an app for product creation or subscriptions, when the cart is submitted it's intercepted and sent to that apps backend to be processed they send requests to the shopify api get the results back THEN send data back to the customers browser THEN the cart/checkout is created.
To remove such a loop build features into themes directly as possible.
Beyond that would be open ended network debugging, or speed auditing a website beyond the scope of a forum post to dial in ambiguous problems.