Following the recommendation of the author in another thread, I installed Version 5.9.15.7 of the plugin. WordPress Links, Menu and widget are back again, but as soon as I deactivate the plugin they disappear!
I have never experienced before that a software developer dares to corrupt WordPress installations or Operating Systems when the user wants to remove his software.
@yannick: Please provide a solution asap!! If you can deactivate the core WordPress Link Manager when activating your plugin, you also can re-activate the core WordPress Link Manager when de-activating your plugin.
Contacting you via your contact form seems not to work for me, this is why I’m writing here.