TLDR at the bottom.
Paradox has been having their online event this week, running through their games, and showing off upcoming content (where appropriate). Their bigger games -
Crusader Kings 3 has a new expansion announced - Royal Court. You'll deal with your subjects while holding court, and get the opportunity to show off your power and splendor through the court room.
Europa Universalis IV - No big announcements, but that's not a surprise as an expansion was released at the end of last month.
Victoria 3 - Yes, I know that people are insisting that the brand new trailer labeled "Victoria 3" means that Victoria 3 is announced and on the way. Ignore this. It's false speculation and hype, and you're just building yourself up for another disappointment. Sorry, inside joke touching on how long people have been waiting for this game, and how desperate some people have been in looking for "clues" about its status. Victoria 3 has been announced. No real news at this date, except that it won't include mana, and that war and "painting the map" won't be the focus of the game (though it will still be important).
Hearts of Iron IV - Teaser trailer for the upcoming Soviet rework expansion, "No Step Back". No real information in the trailer, though. Word right now is that logistics and weather will get a rework in the accompanying free update to become more important in the game. Currently, they're mostly an afterthought unless your "allies" have placed enough of their useless divisions in your theater to cause a supply bottleneck.
Stellaris - Nemesis was just released, so there aren't any announcements for this game. However, you can play for free this weekend on Steam.
Cities: Skylines - Before PDXCon, Paradox teased that it had something it was working on with Colossal Order, but it's still too early to announce whatever this is. In the meantime, this game is also enjoying a free weekend on Steam.
And drifting to the less notable titles -
Imperator: Rome - Heirs of Alexander was released in February. There haven't been any announcements yet of new content at this year's PDXCon.
Surviving Mars - This game recently got a new pack of useful buildings, though aside from that Paradox seems to have been ignoring it lately. There's a free weekend going on right now on Steam.
Empire of Sin - the disappointing (from what I've heard) game about running your own gang in Prohibition-era Chicago will get a new expansion adding fixers and loan sharks to the game.
Note that the event isn't over, so more announcements could still be made.
TLDR - Stellaris, Cities: Skylines, and Surviving Mars free to play this weekend on Steam.
Victoria 3 announced.
Expansions announced for Crusader Kings 3, Hearts of Iron 4, and Empire of Sin.