@fabrice-theveny
Thanks for reaching out. There are several grey areas that might be behind the issue that you are facing, let’s try to initiate the debugging process:
– switching to the default theme to rule out any theme-specific problems.
– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.
– re-uploading all files & folders – except the wp-content folder – from a fresh download of your current version of WordPress. Make sure that you delete the old copies of files & folder before uploading the new ones.
Resource: https://www.ads-software.com/support/topic/500-internal-server-error-updating-adding-plugins?replies=14
Let me know if either of the above helps your case else we would try other options too.
Awaiting your response.
Regards,
Sandeep
