If you deactivate a group, it will no longer be displayed in your group overview. In this case, the group is not deleted and can therefore be reactivated.
Important : A deactivated group disappears from the group and chat overview for all the users, not just for yourself. If you want to hide a group from only your chat overview, you can archive the chat. This is then only hidden for you and appears again as soon as a message is sent to the chat.
You can reactivate a group by opening your group overview. Here you will find the option "Deactivated Groups".
Select the group that you would like to reactivate. In this group click on "Settings" and then on "Activate group". This will then be displayed to all members again from now on and is available again in the chat and in the cloud.
Only the admin of a group can deactivate it.