I found a post with a great advice to solve the graphic issues.
https://en-forum.guildwars2.com/topic/130128-have-played-the-game-since-launch-until-april-18/?do=findComment&comment=1886591
For me this works great. I added these options and everything looks beautiful like before.
In addition, my Windows key now works again ingame, so that I can for example call up a guide in my browser directly from the game, like before the last update.