indesign canvas can not be 6500mm in CC
can not create a canvas with 6500mm, it reverts back to 5486.4 mm
As an industry standard software, you would expect that there is no limitations to the canvas size.
Six and a half metres is a very high limit. From experience, file sizes can get huge at this scale. When I'm designing bigger than that I design at half-size and even quarter size. What are you trying to produce?