Because of the use or Uri class (don't know why ...), application path containing spaces (e.g. ClickOnce deployed app running on a user account with spaces) produce the following exception when trying to connect to DB with compression enabled:

System.IO.FileNotFoundException: Could not find library snappy64.dll. Checked C:\Users\User%20Name\source\repos...\bin\Release\net5.0-windows\snappy64.dll;C:\Users\User%20Name\source\repos...\bin\Release\net5.0-windows....\runtimes\win\native\snappy64.dll;C:\Users\User%20Name\source\repos...\bin\Release\net5.0-windows\runtimes\win\native\snappy64.dll.

The request here Can't make use of compression when application path contain space by jeremy-waguet · Pull Request #457 · mongodb/mongo-csharp-driver (github.com) does fix it. For now I have to disable compression on the connection string (to keep using official nuget packages)