Because i cannot start the christmas chronicles on GOG galaxy. is there a version of the Christmas Chronicles with JJ2+?

When you buy Jazz Jackrabbit 2, you get two separate games: The Secret Files and The Christmas Chronicles. They should each show up as separate items in your library (i.e. just installing the main game does not include the Christmas content -- you have to specifically install The Christmas Chronicles to get that).

I can't help with Galaxy since I never use it, but if the Christmas Chronicles doesn't install properly through Galaxy for some reason you can just download the offline installer from the website: https://www.gog.com/account

If you use the offline installer, Galaxy should detect the game -- or you can add it to Galaxy manually. (Again, I'm not entirely sure how it works -- I only used Galaxy long enough to realize it wasn't something I wanted or needed.)

There is not a jj2+ version of the christmas chronicles. It has nearly the same features as The Secret Files and not many people own it, so it was decided to go with the more popular release.

However, since the versions are nearly identical, what you can do is copy levels (*.j2l), tilesets (*.j2t) music (*j2b) and episode (*j2e) files from the christmas chronicles to the secret files folder. The levels will work perfectly fine with the secret files and jj2+.