flatpak "download only" update location

In APT, we can do apt upgrade --download-only so we download locally without installing. In flatpak, according to their help, we may use flatpak update --no-deploy to achieve the same behavior: "Don't deploy, only download to local cache" The problem is I can't find it. I used verbose during flatpak update --no-deploy command, and it shows: flatpak_dir_pull: Using commit [...] for pull of ref app/[xxx]/x86_64/stable from remote flathub Tried to find and grep this [...] commit, could not find anything (grep is still running). Does anyone know where is this "local cache" ?