After several days of studying the site, I write about my problem.
I installed the server without issue on ubuntu-20.04.1-desktop-amd64
Displays were also installed, one xibo player on ubuntu-20.04.1-desktop-amd64 and the second on win 7x64 (with the client xibo-client-v2-R202-win32-x86).
Also, as a test, linuxmint-20-cinnamon-64bit with a package of codecs and vcl was installed on the third display.
Everything would be fine, but the video, previously converted to webm and mp4 (I tried it in different ways by reading the solutions to the problems on the site) using HandBrake and WinFF reproduced only the display on win 7x64.
The problem is that:
On ubuntu-20.04.1-desktop-amd64 with a pack of codecs and vcl (and mpc just in case), no video is displayed, a black screen, or a black screen with hieroglyphs in the center of the screen.
On linuxmint-20-cinnamon-64bit with a package of codecs and vcl, the video did not start, giving out at first the player error 12, then indicating that it could not load resources (404 error)
Question: on which version of Linux (no matter the manufacturer) I can run video on the display through the server without problems and difficulties, just as I can now on the display with win 7x64.