Thanks to both of you for your assistance. And your are both right : raspbian use the debian package, but the raspbian team have to compile them from source for ARM that is a RISC processor. Furthermore, the raspbian team made a hard work to make a patch for the GPU (OpenGL driver).
For the backport, I had difficulty to find source.
I tried to test 5.1.6 from the bullseye repo (just for the fun I have to said because 5.1.6 is testing)
#deb http://raspbian.raspberrypi.org/raspbian/ bullseye main contrib non-free rpi
I updated only kicad and dependencies (new version of python mainly) and saw kicad 5.1.6 running on RPI. But then LibreOffice was broken because of python. I had to manually remove packages (python and kicad) and reinstall them from buster repo.
I tried to upgade all the system to bullseye, but the system hade big problem with the windows manager.
In summary :
When I updated kicad from 5.0.4 to 5.1.4 on the RPI (a week ago), the improvement was significant : implementation of the modern toolset (accelerated) for pcbnew (I noticed a real improvement in speed) and the cursor bug was solved.
I can work on my last design that is a 300 components size. Pcbnew run fast on RPI if the size of the windows remain lower than full screen on a 4k display. (this is not a problem for me as I use half screen for pcbnew and half screen for eeschema on a 43” screen)
I think I can continue the work with kicad 5.1.5 on Ubuntu and 5.1.4 on Raspberry (Both machine are synchronized with syncthing). This little difference of version should not be a source of problem as the files format remain the same.
I think the kicad team made an amazing work! And this is for me the occasion to thanks them : I made professional design in university with this software. Kicad do the job for complex design with a fast learning curve (compared to the other heavy commercial soft.)
When the bullseye raspbian will be stable, I will be able to use 5.1.6 under RPI. This is why if 5.1.5 isn’t yet on RPI, compile from the source would be a wast of time for the kicad team as they would prefer focus effort on the new 5.1.6 for all platform (I guess)