Also raving about Squarespace Websites Tools Extensions. Just moved 318 blog posts from one 7.0 website to another (You can also move from 7.0 to 7.1.). This took a few minutes to set up, and the transfer completed in about 15 minutes, saving me weeks of work. I've had two websites for a while, and have been wanting to merge them, but dreading the time commitment involved. No more. It's done! .
This tool currently (as of Jan 2022) operates on a subscription model, of which there are two levels. I signed up for a 5 day free trial, but they offer a few other interesting plugins, so it may be worth it to continue with paid subscription. Watch their intro video, install the plugin, and you'll be good to go. There's also a slack channel for support.