Ok, I made some progress
I tried Assets -> Open C# Project from Unity, that didn’t help.
I then looked at the actual output (thanks a lot greg-harding for pointing out that I needed to look at the Omnisharp output). I googled the errors I saw there and it aligned with Kurt-Dekker’s second link ( No suggestions in Vscode ) and greg-harding’s suggestion - mono is needed. I went to Download - Stable | Mono, clicked on Download Mono 64-bit (no GTK#), and installed Mono. I reopened my C# file (using open C# project) and now using UnityEngine and MonoBehaviour is recognized, but “Tile” still isn’t. I tried using GameObject and that is recognized though.
I didn’t run export FrameworkPathOverride=/Library/Frameworks/Mono.framework/Versions/Current in Kurt-Dekker’s second link , I wasn’t sure where I was supposed to run that command. I couldn’t run it from the VS code terminal, Windows command prompt, or the Mono command prompt. Where can I run this export command?
I also did not see any Use Global Mono setting, but I did see a Omnisharp: Mono Path setting that seemed to be relevant. Does that need to be specified, or is this Tile error not relevant to Mono? I am still seeing the The type or namespace name 'Tile' could not be found (are you missing a using directive or an assembly reference?) error in Unity.