bonjour, je n'ai plus les vignettes photos

It seems your monitore profile has a fault.

Please look here: How do I change my monitor profile to check whether it’s corrupted? | The Lightroom Queen

Have you considered that your preference file may be corrupted and needs to be "reset"

The preference file can get corrupted leading to buggy behavior. A corrupt preference file will survive uninstalls, updates, and upgrades. By renaming or moving or deleting the preference file you create a situation where LrC will recreate a fresh new one upon startup of LrC. Be aware various settings will revert to defaults.

https://helpx.adobe.com/lightroom-classic/help/setting-preferences-lightroom.html

https://helpx.adobe.com/fr/lightroom-classic/help/setting-preferences-lightroom.html