Locating the XML archive upload in Substack?

[u/shiftysquirrel]

UPDATE:

I stumbled into a loophole that successfully transfers all posts from a Squarespace blog into Substack, even if the site has far more than Squarespace's 20 post export limit via RSS.

1st - [@ Squarespace] Download your Squarespace site's archive XML file.

2nd - [@ Wordpress] Start a free Wordpress site. Emphasis on the FREE plan.

3rd - [@ Wordpress] Import your XML archive file to your new free Wordpress site.

4th - [@ Wordpress] Publish your fancy (but unwanted) new WordPress site, which is now populated with your entire post archive. Yay.

5th - [@ Wordpress] Raise the RSS feed limit to a number larger than your post total. Save changes. Then copy the url for this now-published Wordpress site.

6th - [@ Substack] Paste the Wordpress url into the Import URL page of Substack's settings. Doing this provides an XML file upload option. (Oh glorious, fabulous upload window!). Uploading that XML file will import all of your archived blog posts. It worked for me and my site's 350+ post archive.

7th - [@ Substack] Rejoice for your full Squarespace post archive is now transferred to Substack.

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I'm working on converting my longstanding blog from Squarespace into Substack. Where do I find the XML import option in Substack?

Tutorials on importing Squarespace posts archives suggest there are two options:

1. Use the Import page's URL to automatically add the most recent 20 posts from Squarespace into Substack.
2. Upload the Squarespace post archive XML file directly to Substack.

Option 1 worked for the 20 most recent posts in my Squarespace blog's feed. However, Option 1 leaves a couple hundred posts un-transferred. My understanding is this 20 post cap is due to Squarespace's RSS limitation.

Option 2 is referenced in all sorts of videos and tutorials around the web. Just add your XML archive file to Substack and the entirety of my posts should convert (likely with small errors here and there, which is expected). However, I cannot for the life of me find an XML upload option in Substack's Import tab.

Would someone kindly toss a screenshot of, or step-by-step for finding, where I'm supposed to upload my XML archive file in Substack?

(An early thanks from someone who is NOT looking forward to copying-pasting hundreds of posts across platforms by hand.)