Worlds Are Complex
There are two main styles of 'handout' that I endorse. One is informational - 'This Is What Your Character Knows', i.e. information focused on the nation they grew up, facts about life, working, families, how much magic there is in the world, poor people and rich people, kind of names you'll have depending on where you grew up. Races, race tensions. Street-level stuff.
The other is in-game documentation. For investigatory games this can be files, photographs, police reports. For Eberron, it could be a pamphlet talking about the wonders of , a church propaganda flyer about the terrors of the wastes, an 'informational pamphlet' extolling the virtues of one of the merchant Houses, etc.
Anything overarching or beyond that, should be presented in-game. Shown, not told. Otherwise it removes the growth of characters learning stuff in character, which is like 99% of the point of roleplaying vs collaborative storywriting. Background info, or stuff that is a facsimile of stuff their character is looking at - that's my rule.