@guru UBUNTU TOUCH v4 ** IS ** OTA 5 : I updated last night OTA 3 STABLE /OTA 5 STABLE on a BQ 4.5. But I had to desinstall some vivid app which were on the phone yet and didn't work. For the equivalent xenial of vivid apps, they were updated. I noticed that vivid WALLPAPERS app works well on the xenial phone ! And download wallpapers is possible.

After installing these packages it finally worked. Glad to use ubports ubuntu now Looking forward to use updated apps and hope it will be stable as canonical version was. And this installer is not finished, neither snap nor appimage formats work on regular 18.04 computers without these additional packages installed. Thanks everybody for help.