Upgrading Drupal

After upgrading from 8.5.6 to 8.6.1, I am unable to update the site. I get the following error message (translated to english):

I have been racking my brain all weekend on this and hope that someone can shed some light on the best approach to accomplish a this task. I am building an HR system for my company and have employees (user entities) that work at different locations. Each location has an HR rep that should only see the employees who work at their location. In addition there are corporate employees who can see all employees no matter what their location.

Hello,

i have a big problem when i run UPDATE.PHP after 8.70 to 8.71 :

==>

"Mettre à jour make_menu_link_content_revisionable

Hi guys,

Last days spending alot of time creating a website in drupal 8. I used a premade theme from DrupalExp: https://www.drupalexp.com/themes/nation

Now my website is almost done just wanted to integrate some security measures starting with updating to the most recent version.

I have update my site to latest  version (Drupal 8.7.1). But according to Patchman on my server, it still complains about a security issue:

Input Validation vulnerability in Drupal
/home/injuryclaims/public_html/core/modules/serialization/src/Normalizer/NormalizerBase.php

Should this be ignored?