SharePoint Authentication from C# Application

I've been struggling a bit to get authentication working. My C# application is a COM-based Add-In for a product called Enterprise Architect. In the app, we want to copy files to/from SharePoint, and to do that, I have to get a ClientContext object for the current user. I'm currently using AuthenticationManager.GetWebLoginClientContext(), but it has started behaving oddly - it has always popped up a browser window, but the window used to go away on its own once the authentication was done. Now that window is getting "stuck" and never closes unless I close it. This is my code:

using ODP = OfficeDevPnP.Core;

ODP.AuthenticationManager authManager = new ODP.AuthenticationManager();
ctx = authManager.GetWebLoginClientContext(ContextUrl);

If I close the browser window, ctx ends up being null.

I have also created a test harness console application that calls through to this same code, and when I run the console app, the browser form does in fact go away on its own, and the code works. But when I exercise this code via Enterprise Architect's COM-based Add-In interface, which  calls code that ends up going through this same exact code, the browser window does not close on its own as described above.

I have also considered switching over to AuthenticationManager.GetAzureADWebApplicationAuthenticatedContext(), but that would require a way of getting an access token. I have found lots of examples online, but they ALL refer to a MicrosoftGraphHelper class that has a GetAccessTokenForCurrentUser() method. For the life of me, I cannot find a NuGet package or anything that has an implementation of this MicrosoftGraphHelper class. For example:

using ODP = OfficeDevPnP.Core;

ODP.AuthenticationManager authManager = new ODP.AuthenticationManager();
ctx = authManager.GetAzureADWebApplicationAuthenticatedContext(ContextUrl, (url) => { return (MicrosoftGraphHelper.GetAccessTokenForCurrentUser(url)); });

I never would have expected this to be this hard to figure out - I have burned many hours, finding many false trails related to previous ways of interfacing with SharePoint, many of which are no longer recommended. For example, that OfficeDevPnP assembly import - it was quite a while before I found something that said that SharePointPnPCoreOnline is the currently recommended way of integrating to SharePoint, and other ways are not recommended because they are no longer being maintained.

Perhaps the best course of action would be for someone to recommend a good tutorial for basic integration from C# to SharePoint Online.

Help!