nice lag 40 fps

You can transfer the vanilla saves to seamless coop, although you can't do it the other way around. If you are concerned about that, you can use Cheat Engine to make another character that is a clone of your original character, and as long as you don't use Cheat Engine while online, you'll be fine. https://www.cheatengine.org/

I think there's no way to transfer the Seamless coop save to the normal game.

It lets you play with friends without getting invaded

Download Seamless Coop then, here's the link https://www.nexusmods.com/eldenring/mods/510

you invaded me? and it was on ds3 or elden ring?.
Anyway, I don't like being invaded, I just want to play with my friends or alone.