As the creator of the mods "Flags of the Soviet Union" and "Flags of Fraternal & Other States", I warmly encourage you to read the descriptions of the two items. They contain an exact explanation of what you need to do to have the flags available in-game.

I would also like to say that you should probably put questions directly relating to specific mods in the comments of those mods. I happen to often check the Steam discussions, but most modders absolutely do not.

Another thing is that the building menu can only show up to a certain amount of items. If there are more items than the limit, they can only be found through the mod menu on the left side.

https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2823141415&searchtext=polish+posters I could't get it to work both skins for it dosen't work in game and there is no base for re skin