Yep, same here. Started a new sandbox game recently with Retribution which I purchased prior. Then just researched Xeno entertainment as humans (slightly modified by myself but still allows xeno entertainment). Yet I can only build the entertainment capital. The center is not in the planetary buildings list. Without that my morale is pretty much down and it is hard to continue the game. Looks like a bug. I can upload the savegame if needed. I never use any mods as the stock game is great as it is.

You're right. Thanks for the hint! Something to get used to as usually the successor buildings follow the same tech line. So cultural exchange needs to be researched first to build the ent. center and before entertainment network can be built as improvement.