First of all - yes I realize that Dorico has not yet officially supported macOS Sequoia. Being the Apple rebel that I am, I went ahead and installed macOS 15 on my Apple Silicon with Dorico 5.1… So far, I’ve only encountered one single issue with Sequoia (granted that I DO NOT use all the possible features of Dorico just yet) - the print dialog. Dorico’s print dialog “zone” is a bit dodgy controlling the printer. Specifically, sometimes it changes the page range so that page 1 is no longer showing in the print preview. And, the duplex feature control is not communicating with the print driver at all.
I’m sharing this as a “bug” (using the term loosely since Steinberg has not sanctioned Sequoia) that could occur when upgrading to Sequoia. The work around has been to use the System Dialogs to control printing or to save as a PDF and print the PDF.