bookworm Installation fails with “unmet dependencies” Error

$ apt install bookworm
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:
 bookworm : Depends: libgranite3 (>= 0.2.0) but it is not installable
E: Unable to correct problems, you have held broken packages.

$ apt policy bookworm libgranite3
bookworm:
  Installed: (none)
  Candidate: 0.6-0~42~ubuntu16.04.1
  Version table:
     0.6-0~42~ubuntu16.04.1 500
        500 http://ppa.launchpad.net/bookworm-team/bookworm/ubuntu xenial/main amd64 Packages
libgranite3:
  Installed: (none)
  Candidate: (none)
  Version table:

$ lsb_release -sd
Ubuntu 16.04.3 LTS

I contacted the developer behind ppa:bookworm-team/bookworm, but apparently he doesn't maintain bookworm anymore. Instead he pointed me to ppa:bablu-boy/bookworm-daily, where the software is availabe in a maintained state.

To deinstall (traces of) the old program and remove the faulty PPA, follow these steps:

• deinstall the program

  sudo apt remove bookworm
  

• remove the old PPA

  sudo add-apt-repository -r ppa:bookworm-team/bookworm
  

To add the new PPA and install the program, do:

• add the new PPA

  sudo add-apt-repository ppa:bablu-boy/bookworm-daily
  

• update the package sources

  sudo apt update
  

• install bookworm

  sudo apt install bookworm
  

This didn't work for me. It failed with an unmet dependency on libgranite4.
I was able to get bookworm to install by adding the repo ppa:elementary-os/stable, which I found in this post.

Their website has a workaround for this issue. What you need to do is to add the elementary-os repository to apt-get as well:

sudo add-apt-repository ppa:elementary-os/stable
sudo apt-get update
sudo apt-get install com.github.babluboy.bookworm

Then (according to their website) you can remove elementary-os if you'd like:

sudo add-apt-repository -r ppa:elementary-os/stable