You can invade other people without them wanting it yeah.
It can at time lessen the enjoyment of the game since you can be griefed by being invaded at difficult places. Assume that is even more so now that it is open world with lots of bosses there. Peeve did a whole thing in the network test where he invaded people in the middle of fighting the first open world boss you encounter.
That said, they also have mechanics in place to help you, like people of the blue covenant, who if they wear their covenants ring, gets auto summoned to help people who get invaded. They're the blue spirits, invading are red. This is in souls games though, but assume there will be something similar in Elden Ring.
Or you can turn it offline and not have invasions (and lose multiplayer text messages, and also lose the ability to summon help if you need it).
I remember trying to coop Bloodborne with a friend, who doesn't like the difficulty of the bosses so much and banging his head against the wall, but does like the themes, fantasy and exploration. Flat out quit when we got to the section where there all these bell ringing ladies are (some of them hidden) which caused constant invasions. Not being able to progress or have to change your play (from taking your time exploring and such) due to invasions was not fun for him at all. And I can see that.
I'd actually love a setting to where I could coop Elden Ring with him at the same time as turning off all invasions from other players. We've done coop in games since we were kids, but he isn't touching a souls game again. He hated invasions and is now under the impression that only asshats PvP in those games out to ruin other peoples enjoyment. And hard to say that many aren't. At times when I get invaded I go into "lets go!" mode, but a lot of time time I don't want it, and they wait until I start getting attacked by something else to start fighting. That is something I've always hated and never thought was a good mechanic. That PvP invasions are counted as an "enemy" and don't npc aggro enemies. That whole part is just a "how can we make PvPers able to grief and annoy even more!" design decision.
That said, I don't think I've ever done offline mode. It just feels "wrong". But, depending on just how griefable it now becomes as there are so many bosses in open world (PvPers despawned if you entered boss rooms in the souls games), I might change that for Elden Ring. (Feel bad for PC players if they get the "hackers" again though which instantly destroys all your gear or drops items which break your game)
