You shouldn’t need the installer file in order to compile a .kmp keyboard package for installation. The only reason you’d need the .msi installer file is if you want to create a bundled .exe installer. Typically, instead of doing that we recommend that you prepare your keyboard package for upload to the Keyman keyboards repository so it can be distributed from the Keyman website.
However, if you do want to deploy the Keyman installer along with your package as a single bundled executable file, you can extract the .msi installer from the keymandesktop-10.0.1201.0.exe (or any version) with the command line:
keymandesktop-10.0.1201.0.exe -x <path> (where <path> should be the name of the folder to extract the files to). Read more