If you need this type of automation built then contact me for services
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ALWAYS please provide context, examples: store url, theme name, post url(s) , or any further detail in ALL correspondence.
You can use the Bulk Operations feature in Arigato Workflow Automation to automatically add the 5000 products to the custom collection in just a few clicks. With this feature, you can add a custom filter to search for products created in a certain time frame and have the workflow add them to the collection automatically.
Please feel free to drop us a line if you have any questions or if you need help with the configuration.