Okay, well it was indeed a framebuffer problem.
As I am lucky to have a fairly common configuration, my EFI folder containing clover came from a step-by-step guide for this configuration. The configuration of the framebuffers was sufficient until now, but was no longer correct for 10.15.5.
By literally returning Google, I arrived on a German forum, which gave the solution ... Just reproduce this configuration for the framebuffers, the ig-platform-id and the device-id.
I am now on catalina 10.15.5, and I have my 4 screens, as originally. Now I just have to reconfigure everything as it was .... so I installed a new hard drive to configure a TimeMachine ... I would no longer have ^^
Marked as solved !
