I have items/buildings that are showing up in quest rewards and I'd like to prevent it. They already have the <tradeability>None</tradeability> set, but the game appears to ignore this for quest rewards.
What is your goal for this?
Do you want that building to just never appear in the game at all?
There is no way to prevent the game from generating an item or minified building using only XML.
Unfortunately each of the different types of quests has their own version of ItemCollectionGenerator_Rewards. The only way you could safely remove it from all quest rewards would be to either patch ItemCollectionGeneratorUtility.Reset() to keep it out of the main list, or patch each of the quest types to reject it as a possible reward. There really should be a tag that you can apply to let the game know that an item or minified building should be exclusively craftable.