If you're achievement hunting, you'll need to find those mods that will tell you in their descriptions that they're Ironman compatible.Finally, sometimes it takes a while for the HOI4 interface to properly load the mod's latest version. This information is usually found on each mod's page as they usually list which mods they are able to run with.Remember that most mods are not compatible with Ironman as they change game balance. If all else fails, ask in the comments threads for instructions!Check if the mods you've selected are compatible with the other mods you've downloaded. Check the mod pages on Steam or the Paradox forums on how to do this since it might be different for each mod and version of the game. Also, each mod will tell you on the side menu if it requires certain DLC.Still want to play that favourite mod of yours but HOI4's latest update ruins your save game? You can always roll back your HOI4 version to continue your campaign.
Thankfully, HOI4 will give you a warning if you're about to load a mod that isn't up to date. Once a new expansion comes out you may have to wait a few days, weeks, or even months for bigger mods, until the mod is updated. How to Mod Hearts of Iron 4Check if the mod is up to date with the most recent patch for HOI4 (Currently 1.9 Husky).