Fixed in 1.2.1: startup on HFS startup disks.
System 6 opens the startup application of an HFS disk only from the System Folder. If the application is anywhere else, the Mac starts the Finder. startup used to accept an application in the root of the disk and report opens "App", but the Mac then booted into the Finder (checked on a Mac Plus with System 6.0.8).
startup now looks only in the System Folder and says how to put the application there: mac68k-disk add Disk.dsk App.bin --name "System Folder:". info and startup also report a startup application that is missing, for example opens MultiFinder (not in the System Folder: the Mac starts the Finder instead). MFS disks are unchanged.
Install: sudo apt install ./mac68k-disk_1.2.1_arm64.deb (or _amd64.deb), or brew install bircher988/tap/mac68k-disk.