lighthttpd won't install - Depends: libssl1.1 (>= 1.1.0) but it is not going to be installed

I've been trying to install lighty on my PC running Ubuntu 18.04. The error I keep getting is that it has unmet dependencies, namely libssl1.1. However, libssl1.1 is already installed.

   $ sudo apt-get install lighttpd
      Reading package lists... Done
      Building dependency tree       
      Reading state information... Done
      Some packages could not be installed. This may mean that you have
      requested an impossible situation or if you are using the unstable
      distribution that some required packages have not yet been created
      or been moved out of Incoming.
      The following information may help to resolve the situation:

      The following packages have unmet dependencies:
       lighttpd : Depends: libssl1.1 (>= 1.1.0) but it is not going to be installed
      E: Unable to correct problems, you have held broken packages.

The output of apt-cache policy libssl1.1 is

libssl1.1:
  Installed: 1.1.1a-2+ubuntu18.04.1+deb.sury.org+1
  Candidate: 1.1.1a-2+ubuntu18.04.1+deb.sury.org+1
  Version table:
 *** 1.1.1a-2+ubuntu18.04.1+deb.sury.org+1 500
        500 http://ppa.launchpad.net/ondrej/php/ubuntu bionic/main amd64 Packages
        100 /var/lib/dpkg/status
     1.1.0g-2ubuntu4.3 500
        500 http://zw.archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages
     1.1.0g-2ubuntu4 500
        500 http://zw.archive.ubuntu.com/ubuntu bionic/main amd64 Packages

I'm not sure if there's anything I might be missing here.

I see two options:

• Try to install libssl manually (the exact version from official repository):

  sudo apt install libssl1.1=1.1.0g-2ubuntu4.3
  

• Remove ppa:ondrej/php from the system:

  sudo apt install ppa-purge
  sudo ppa-purge ppa:ondrej/php
  

  and then install lighttpd

  sudo apt install lighttpd