The bug with throwing "bufferAdapter is not a VsTextDocData" when saving a model in .NET Core, .NET Standard, .NET 5, .NET 6 projects of Visual Studio 2019 is fixed in dotConnect for MySQL v8.19.1866:
viewtopic.php?f=2&t=45001.
Be aware of a side effect caused by our fix - the diagram window of a model is not marked with the asterisk in its tab title in Visual Studio after the model has been modified. We will look for a solution to this issue.