The lag isnt due to the server, its due to trying to synch all the players together with their different connection speeds etc, which is necessary when theyre in the same area. If you spread out the lag will go away till you come back together again.

I usually see slots tied to RAM. Your dedicated server hosted only 4 people which makes me think it had very little in the way of RAM which will cause a lot of lag, especially when more people are present.

I'm just going off the information you've given. I don't know what your server actually offered beyond that.

Lag still happens, I get this a lot on my friend's server. If mods are your thing, grab the Better Networking mod (all players need it) and manage your settings through that. It's a life-saver.

Networking was changed since initial release (from Steamworks to a P2P system), much less laggy in general though it still doesn't scale particularly well.

Terrain modification - which used to cause severe lag problems in the initial EA release version - now has a new tracking system that is both less system intensive and network intensive. You now have to commit some pretty major terraforming projects to notice the lag.

Are you sure the problems you faced were not related to the hardware specifications of your server?
I'm running a dedicated server and it works great, no lag problems whatsoever. I believe the code for Valheim server is solid enough, but keep in mind that if you build large structures and bases, the game will suffer from framerate drops and that is not related to the server but to bad optimizations in rendering.

I m 100% sure yes there are many network " fixes" on Youtube so i m not the only one with this issues

Well, I didn't know that. Anyway, I can only report my own experience and it's been great on my side. The game is still on EA, though, and they can always improve things.

Yes they can thats i was wondering if they maybe did :D. But maybe i have to Test it again

The more you modify the terrain the longer it takes to load. If you build a huge base you are going to experience lag in the late game.

Okay so they Changed nothing okay but thats fine so we cant build a Viking Village again.

After the Server was Laging i Tested to Host on my PC and i have no Lags but all my friends got the same Lags like on the Dedicated Server. So they tested what happen if the Host and we got the same Problem no Lags on the Host but all players that join got Lags