The installer will scan your existing folder, verify all files, and only download what's new or changed. After the update is complete, you'll need to copy the updated folder back to your offline machine and run the installer again to apply the updates.
: Run this in your command prompt to download only the necessary .NET desktop workloads (saving roughly 15GB of space compared to a full download): vs_community.exe --layout C:\vslayout --add Microsoft.VisualStudio.Workload.ManagedDesktop --lang en-US visual studio 2019 offline installer
To focus strictly on web development, ASP.NET, and cloud applications: The installer will scan your existing folder, verify