Yes, defeating each boss will disable a certain enemy spawn during an event.

https://valheim.fandom.com/wiki/Events

If you haven't defeated Eikthyr, then the only event you should see is "Eikthyr rallies the creatures of the forest". Once you defeat Eikthyr, you will not see that event anymore.

Once you defeat Eikthyr then you can see "The forest is moving". Defeating The Elder will disable this.

If you kill a Troll or the Elder, then you can see "The ground is shaking".

Also, after defeating the Elder, you can see "A foul smell from the swamp". If you haven't defeated Bonemass yet, then you should expect to see Draugr and Skeletons. If you have defeated Bonemass, the you should only see Blobs and Oozers.

After defeating Bonemass, you can expect to see "A cold wind blows from the mountains (Drakes), (along with "A foul smell from the swamp" (Blobs), or "Skeleton Surprise" (Skeletons/Rancid Remains). If you have killed a Surtling as well as Bonemass, then it's possible to see "There's a small of sulfur in the air" (Surtlings). If you're in the mountains or plains, then it's possible to see "You are being hunted" (Wolves) as long as you've already defeated Bonemass.

I've been drinking, so I apologize if this is hard to understand but I refuse to proofread at this point. If you're still not sure, check the wiki/Events page. Once you've defeated all bosses in a specific world, the only attacks you should see are Trolls, Blobs, Skeletons, Surtlings and Wolves.