Visual Studio not autocompleting methods from monobehaviour

Well, first of all the $$anonymous$$onoDevelop methods like Update, Start, .... are not overridable methods and therefore won't show up in any normal intelli sens autocompletion. Those are called based on the name of the method through reflection by the engine. You have to have the Unity development tools plugin installed in your Visual Studio. Those provide autocomplete for the "Unity $$anonymous$$essages". This feature can be turned on / off in the settings menu of Visual Studio under the category "Tools for Unity".

Note I don't have VS 2019 but I'm pretty sure there are Unity tools for 2019 as well. You can check if they are installed by clicking "Tools" -> "Get Tools and Features" inside Visual Studio. This brings up the Visual Studio installer. Under workload you should see the Unity tools already installed. If not, install them. It should be named something like "Game development with Unity". $$anonymous$$y installer is in german, so I can't say what it's called in english ^^.

If there are no Unity tools available, you don't get autocomplete for those messages in VS 2019. You might need to wait until they provide them or just use VS2017. I still use 2017 for almost everything.