Thank you very much Sam,
you give me the clue to solve it . Unreal 4.26.2 is working properly now.
In fact I have just upgraded the drivers install on my PC and after installation of the last NVIDIA drivers Unreal 4.26.2 works.
Below the procedure apply on Ubuntu 20.04.02 TLS if people have the same issue :
sudo apt update && sudo apt upgrade -y
sudo apt autoremove
sudo ubuntu-drivers autoinstall
Now I have these drivers installed : NVIDIA Corporation GK208BM [GeForce 920M] / GeForce 920M/PCIe/SSE2.
Previously I have : NV106/MESA Intel HD Graphics 5500 (BDW GT2)
Kind regards
PhilippeC
