How to add a module to an existing game 2022

I see this has been asked before as far back as 6 years ago. If this functionality isn't in the game already I will actually be a little surprised. I am hoping my search skills have degraded along with my capacity to read as to the reason I haven't found the means to do this in 2022 without having to jump through Pro hoops (I have Pro, but not the point). Here's an example just so my use case is clear. We have an existing campaign we've been playing for years, but now I want to use some information from Descent into Avernus (thinking about having our character's children take up the mantle of adventurers in the same world). Ideally I can just suck in the whole module into our existing campaign so I can pick and choose what I need, instead of importing a chapter at a time or anything like that. Hope that explains what I'm expecting to be able to do. Thank you for any assistance!

You can’t add a full module (a game can only be built with a single module), but you can create the second game (DiA) and use the  Transmogrifier  to move assets to your current game. 

This is by design, to keep games from becoming unworkable due to size. This behavior is unlikely to change in the foreseeable future.

Interesting, and a valid concern I overlooked. I must be one of the few people that has purged stuff out of the campaign that was no longer needed - it becomes unwieldy having to scroll through all that stuff, not sure how people get along without purges to keep themselves sane. Maybe the Orr Group folks can consider allowing it for games which do not already have a campaign/module attached to minimize that risk.

Another great suggestion for you (since you have a Pro subscription) is to create an 'Archive' game, and transmogrify things into it when you're done using them in your regular game before you purge them.  That way on the off chance you do end up wanting to reuse something later, you can just transmogrify it back into your regular game without having to recreate them. I have a prep game where I can set up maps and tokens and things, my regular game where we play, an archive game, and a test game for trying out new macros or scripts that I'm not sure I want to use yet or I want to optimize first.

The way of working that i ended up with (and that now works for me): For each module and gameaddon i create an Out of the Box Game. For each adventure i create myself i make a seperate Master Game. For each party i have a separate play game that is kept small  During preparation maps and monsters that will be needed are copied over using the Transmogrifier. During play i have two different browsers open (ie firefox and chrome). In one the play game is open, in the other the OOTB of the module with the story If needed handouts and other items are transmogrified over during play It might seem cumbersome, but i GM three games a week and with some helpers (like a list of monsters to games) it has become so familiar that i even dare to improvise encounters. 

The need to purge a game with too much stuff is one of the reasons that adding a module is intentionally blocked. But yeah, echoing an Archive game, also called a Library game. Besides being a handy place for offloading, it's a good place for general backup.