That's the file format for an object graph serialized by the NSKeyedArchiver API. As you've found, it’s built on Apple's lower level property list structure, which uses XML, but it’s definitely not intended to be human-readable. The format isn't officially documented that I know of, but a quick search turned up these pages that may be helpful:
https://www.mac4n6.com/blog/2016/1/1/manual-analysis-of-nskeyedarchiver-formatted-plist-files-a-review-of-the-new-os-x-1011-recent-items
https://digitalinvestigation.wordpress.com/2012/04/04/geek-post-nskeyedarchiver-files-what-are-they-and-how-can-i-use-them/
There are a few approaches you could try. The various tools referenced from those pages purport to convert this format into something more usable, though you'd still need more processing to yield your data in the format you want, using the programming language of your choice. Or you could try to reverse engineer the app's data model from the metadata in the file (class names, inheritance, and member names) and then mock up an equivalent data model in a Swift program to deserialize the file directly.