It's likely a mod issue. Yesterday Stellaris was crashing on my Mac and someone helpfully traced it to the Improved Topbar UI mod. That was patched by the mod author today.
There are likely many other mods that need to be updated. You can check your mod list against the updated mod thread on the forums, or on Steam go and check your subscribed items to see which ones have/haven't been updated (not every mod needs an update).