I have tried to use Preview to combine PDF files, and encounter spinning beach balls and corruption of my source files. Another package, like KoFax PowerPDF scales well, to PDF documents with thousands of pages and the combination of documents happens within a few seconds.
Preview is not good enough to get the job done for large documents and needs to be recoded.
MacBook Air Apple Silicon
We are fellow users who cannot recode Preview, and the application is not a paid commercial application that might well have the scaling you seek. If Apple did that, then the operating system would no longer be free.
The Finder provides a Quick Action to Create a PDF from selected PDFs. You select the PDFs in the order of combination that you want, and the on the first selected PDF, you control-click and from the secondary menu, choose Quick Actions > Create PDF.
With macOS 12.5, whether Intel or Apple Silicon, this process generates a foo 2.pdf in the same location as the selected combination PDFs, if your first selection was foo.pdf.
macos Monterey: Preview is not scalable or stable
