Problem Installing/Creating macOS 10.15 (Catalina) VM in Fusion 10

[SnakeGirl]

i'm having a problem trying to create a macOS 10.15 (Catalina) VM in Fusion Pro 10:  if i try to use the drag & drop method, i cannot seem to "drop" the Catalina installer file "Install macOS Catalina.app" (only 19.1 MB in size & freshly downloaded from the Mac App store) into the designated space "Install from disc or image"/"Drag your ISO file here to start installing" in the "Select the Installation Method" window.

Can i use a different method such as "Create a custom virtual machine"?  If so, i need some assistance in setting up the installation as i am not familiar w/this method.

Additional notes:  i have been able to create VMs for macOS 10.13 (High Sierra) & 10.14 (Mojave) using the drag & drop method in Fusion 10 & macOS 10.15 (Catalina) is the only macOS version from 10.13 (High Sierra) thru 13 (Ventura) for which i have not been able to successfully create a VM in Fusion 10.  Is there something that needs to be done differently w/10.15 since the installer.app files for 10.13 & 10.14 are 5-6 GB in size & installer.app files for macOS 11 (Big Sur) through 13 (Ventura) are all in the 11-12+ GB size range, yet 10.15 (Catalina) is the only installer.app file which is only 19.1 MB in size?  What accounts for this huge size discrepancy & how is Catalina to be handled differently than the other versions when attempting to create a VM in Fusion 10?

[Technogeezer]

The drag/drop method using the /Applications/Install macOS xxxxx.app is a bit iffy. You may find you will have more luck by creating bootable media from the Install macOS xxxxx.app file than simply trying to drag and drop the app onto the dialog.

See the responses in https://communities.vmware.com/t5/VMware-Fusion-Discussions/Fusion-13-macOS-12-quot-Unable-to-create... - in particular the one by @msschmitt  

If you're running Fusion 10, it's more than likely that you are running at most macOS 10.13 High Sierra (as that's the last macOS version that's supported by Fusion 10). . If you are seeing the installer app of 19 MB, Apple probably gave you what's referred to as a "stub installer" See Mr Macintosh's posting for more info https://mrmacintosh.com/how-to-download-macos-catalina-mojave-or-high-sierra-full-installers/ for other approaches on how to obtain full macOS installers. 

[SnakeGirl]

Wow, so i'm still having difficulty either getting or creating some complete version of the Catalina installer that will enable me to create a 10.15 Catalina VM, i have tried several of the approaches referenced in your reply but still so far am not having much luck & seem to keep running into roadblocks.

What i've tried so far:

The @msschmitt reply from 07-23-2023 03:10 PM to the @pkeller post of 'Fusion 13 / macOS 12 : "Unable to create the installation medium"' from 11-24-2022 in which the hdiutil command in Terminal is used (i have used this method successfully in the past so i am somewhat familiar w/how to use it): after issuing the sudo command, i received an error message of "/Applications/Install macOS Catalina.app does not appear to be a valid OS installer application." even though the Install macOS Catalina.app file was just downloaded it from the App Store.  (screenshot attached)

In Mr. Macintosh's https://mrmacintosh.com/how-to-download-macos-catalina-mojave-or-high-sierra-full-installers/ article,

1.  App Store - already tried & did not receive an installer containing a full OS

3.  Softwareupdate - tried this approach from inside Monterey but kept getting error messages.  i must not be giving the correct arguments such as exact version # of Catalina (screenshot attached)

i'd also like to try the approaches using Github scripts, but i have never worked w/scripts & am not at all clear on how to get access to/download the scripts & how to use them correctly (either the https://github.com/rtrouton/create_macos_vm_install_dmg referenced by @Technogeezer or the MIST macOS Installer Super Tool referenced by Mr. Macintosh at https://github.com/ninxsoft/Mist)

[Technogeezer]

Running Fusion 10 on (what is now ) an ancient version of macOS is making this more difficult.

If you have a more "modern" VM of macOS 11 or later, build the Catalina installer using the MINT tool in that. Then move it back to the host Mac and use that for installation.