[aaronbrethorst]

Can "Summarize selection" work across multiple documents, or is it limited to only a single document at a time?

Also, the Notes app on macOS has a reasonably comprehensive AppleScript Dictionary associated with it for scripting; have you considered using osascript with either AppleScript (ugh) or JavaScript to expand your cross-document capabilities?

[rexec]

Ah yes it's limited to single documents.

Using AppleScript/JavaScript to pull multiple notes is a good idea!