in the past month i can not play different music in different rooms

So what exactly happens, or doesn’t happen, when you try it? This is a basic function of Sonos, and no-one else has reported this issue.

This is definitely still possible. You need to be more specific about how it is failing on your system. 

basically I can not play different music in different rooms.

 But WHY NOT? Literally millions of others can do this.

You state: “To play different music on different Sonos speakers, you just need to select what you want each speaker to play and group the speakers you want to play the same music together. Once grouped, you can select what you want each group of speakers, or singular speaker to play.”

Do I understand it right that you first group speakers (which is what you do when you wnat them to play the same music) to have them all play different music (so they’re not a group after all)? Why?

As asked above: what happens if you tap the system tab, that is different from earlier (and our systems)?

I have the same problem. When I try to play other music in a second sonos music in other room, the music that is playing first in other sonos speaker is stopping. When I try to play the misic again in the first seeker its stopping in the second seeker and so on. There i a solutions for this problem?

Have you submitted a diagnostic, and called Sonos about it? Without any information, my thought would be some kind of wifi interference blocking the ability of the speakers to talk to each other, but there could be other issue that might be revealed by the data in the diagnostic. 

Are you using Spotify Connect or the Sonos app?

Do you have to have 3 or more speakers for this option to work? 

No, the 3 or more requirement applies to pre-defined groups.  A 2 room setup only has one way of grouping, so pre-defining a group makes no sense.  See this link for how to group rooms:

https://support.sonos.com/s/article/3391?language=en_US