Thanks.

I developed that template under VS19, which is why it probably requires it by default, but it doesn't really take advantage of any new features or anything.

Technically, there is no reason at all to use VS19 for XP development, but it happened to be ready for release at about the same time as my first blog article, so I decided to use that, since that was the version people would find at the MS download site. I actually wrote the blog article while using the beta version, and released it on the same day VS19 was released.

Well, there are a few less entities, so it would be marginally faster, but in practice, nothing you would notice.

Won't help you now that you got it working, but I should probably put this into a blog article for future users.

RCV20 is just a macro with a single line, RCVDATA, in it. RCVDATA is a variable holding data sent to CC3+ via intercom. I guess you can populate this variable manually and then call the macro, but it is really a special macro made to handle intercom requests that are CC3+ commands.

The available documentation is the .pdf that comes with the XP toolkit. It is old and incomplete, but that's what is.

As for using C# from an XP, that is actually possible. @saunderl did once write a tutorial about that, but the site is no longer available and the wayback machine don't seem to have captured the actual tutorials. I've been considering looking into that myself, when time permits, but it is fairly low down on my priority list.

You don't have to make symbol catalogs actually. CC3+ is capable of just opening a folder of .png files and displaying it as it was a symbol catalog.

Obviously, you lose all the features symbols catalogs give you, such as groups, random selections, forced sheets, and so on, but for a dynamic collection, the compromise might be acceptable, especially if they have a usable folder structure in this collection.

I do hope they only add items and don't modify/remove existing ones though, as that would wreck havoc with existing maps since CC3+ refers to the image on disk.

Making symbol catalogs for such a collection could actually be a nice community project. The symbols themselves would have to be downloaded from that site by the individual user, but common symbol catalogs wouldn't be a problem if someone could coordinate that and get updated ones out there as soon as the collection changes.