It’s been a 5 years every Merchant and developers asking about Which theme is used by this store?
I found this common Question and now I fix this problem for lifetime. I found a free Shopify theme detector tool that find the exact theme name used by the Store.
Here is the link: https://shopifietools.com/
Cheers 
Thank for sharing this tool here
Thanks for sharing. A quick note for anyone looking up themes: third party theme detectors usually work by scanning the storefront’s source code for common assets or theme_ids. There isn’t an official Shopify tool, and results may be inaccurate if the merchant has renamed the theme or heavily customised it.
You can often see which theme a store is using yourself by viewing the page source (right‑click and select View Source) and searching for theme_store_id or Shopify.theme metadata. This information is exposed by Shopify to support features like Shop Pay but it may not be present on every store.
In general it’s a good idea to be cautious with external tools: don’t enter any private shop credentials or assume the results are 100% accurate. If you need to know the theme a shop is using for inspiration, asking the store owner or looking at the source is usually enough.