IBM Installation Manager wants "gksudo"

Question

I've installed IBM Installation Manager on Ubuntu 18.04 but when I started the following message pops up:

Could not find the program 'gksudo'

I've tried to install it by running the commands below:

sudo apt install gksudo
sudo apt install gksu

But they don't seem to be a part of Ubuntu anymore. I've also read it somewhere. How to workaround the problem?

Adding the universe repository didn't help:

$ sudo add-apt-repository universe
'universe' distribution component is already enabled for all sources.
$ sudo apt update
Hit:1 http://dl.google.com/linux/chrome/deb stable InRelease
Get:2 http://security.ubuntu.com/ubuntu bionic-security InRelease [88,7 kB]

Hit:3 http://ru.archive.ubuntu.com/ubuntu bionic InRelease

Hit:4 http://ru.archive.ubuntu.com/ubuntu bionic-updates InRelease

Hit:5 https://download.docker.com/linux/ubuntu bionic InRelease

Hit:6 http://ru.archive.ubuntu.com/ubuntu bionic-backports InRelease

Hit:7 https://repo.skype.com/deb stable InRelease

Hit:8 https://deb.nodesource.com/node_12.x bionic InRelease

Fetched 88,7 kB in 1s (94,6 kB/s)

Reading package lists... Done
Building dependency tree

Reading state information... Done
All packages are up to date.
$ sudo apt install gksu
Reading package lists... Done
Building dependency tree

Reading state information... Done
Package gksu is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'gksu' has no installation candidate

I also tried to solve it in almost the same way suggested here: https://askubuntu.com/a/1067364/572615

But I created a bash script with the command suggested there (pkexec ...)and created a link /usr/bin/gksudo to it. After that I started the IBM installation manager. The password dialog appeared, but after I entered the password the dialog was closed and nothing else happened.

As a workaround I start the IBM Installation Manager in terminal by issuing the command:

sudo /opt/IBM/InstallationManager/eclipse/IBMIM