For example dotnet package update --exclude System.*

Running dotnet package update will update all packages in a solution, but there are some scenarios where it's desirable to exclude certain packages from being updated.

For example:

• Many customers use LTS versions of .NET and want System.* and some Microsoft.* packages major version to match the .NET version
  • Long term, this scenario will be better served by dotnet package update should support max version ranges #14313
• There might be a package whose latest version is not compatible with the project
  • Long term, this scenario will be better served by dotnet package update should try to select compatible packages #14312
• The latest version of a package might have a bug, so the project needs to keep using the older version for now.