Installing mono on ubuntu: mono-devel : Depends: libglib2.0-0 (>= 2.56.3) but 2.56.1-2ubuntu1 is to be installed

Question

I'm following https://www.mono-project.com/download/stable/#download-lin-ubuntu to install mono on ubuntu. However in the last step I get

sudo apt install mono-devel
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:
 mono-devel : Depends: libglib2.0-0 (>= 2.56.3) but 2.56.1-2ubuntu1 is to be installed
              Recommends: mono-csharp-shell but it is not going to be installed
              Recommends: referenceassemblies-pcl but it is not going to be installed
              Recommends: msbuild but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

My Ubuntu is indeed 18.04. What should I do?

UPDATE:

sudo apt -f install; cat /etc/apt/sources.list.d/mono-official-stable.list
[sudo] password for lz: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  android-libadb android-libbase android-libcutils android-liblog
  android-sdk-platform-tools-common gcc-7-base:i386 libboost-random1.62.0 libboost-regex1.62.0
  linux-headers-4.13.0-21 linux-headers-4.13.0-21-generic linux-headers-4.13.0-36
  linux-headers-4.13.0-36-generic linux-image-4.13.0-21-generic linux-image-4.13.0-36-generic
  linux-image-extra-4.13.0-21-generic linux-image-extra-4.13.0-36-generic
  linux-signed-image-4.13.0-21-generic linux-signed-image-4.13.0-36-generic
  linux-signed-image-generic
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 69 not upgraded.
deb https://download.mono-project.com/repo/ubuntu stable-bionic main