You can do it for example with arcpy.
You need to crate PDF file, then access every single layout in your project, export it and append to the created PDF file.
Your script can look like this:
aprx = arcpy.mp.ArcGISProject("CURRENT")
layouts = aprx.listLayouts()
pdf = arcpy.mp.PDFDocumentCreate(r"path\test.pdf")
for layout in layouts:
page = layout.exportToPDF(layout.name + ".pdf", layers_attributes="NONE")
pdf.appendPages(page)
pdf.saveAndClose()
You can run it directly in ArcGIS Pro Python Window. You need replace "path\test.pdf" string with your real path.