Are there monitors, preferably wall-mounted, where one can upload files e.g. from an USB-stick for a presentation without connection to a PC or Laptop?
There are various media players for ~US$35 and up that can play a presentation in a standard video format, e.g. MP4 or AVI, through a television, if the TV does not already have that capability. If the presentation is in another format, e.g. MS PowerPoint or LibreOffice Impress, you'd need a small PC, such as @CaldeiraG suggests.