Issue with Mathpix-snipping-tool on RHEL8

I went step by step throughout the instruction placed under the following link: https://snapcraft.io/install/mathpix-snipping-tool/rhel.

However the app is not working as expected after clicking select I can see the whole screen as black and particular selection results also with black image. When I run from cmdline the following errors are shown:

(mathpix-snipping-tool:28027): Gtk-WARNING **: Unable to locate theme engine in module_path: “pixmap”,
Gtk-Message: Failed to load module “pk-gtk-module”
Qt: Session management error: None of the authentication protocols specified are supported.

Although could be lunched from GUI without errors.

Checked the mentioned module and it is installed:

$ rpm -ql PackageKit-gtk3-module-1.1.12-4.el8.x86_64
/usr/lib/.build-id
/usr/lib/.build-id/74
/usr/lib/.build-id/74/dde6249da0f03eccefc7a293a0f4fca5b7ae6a
/usr/lib/.build-id/79
/usr/lib/.build-id/79/7866e4abee67d6a641f2457c6e3588705f0211
/usr/lib64/gnome-settings-daemon-3.0/gtk-modules/pk-gtk-module.desktop
/usr/lib64/gtk-2.0/modules/libpk-gtk-module.so
/usr/lib64/gtk-3.0/modules/libpk-gtk-module.so

$ dnf info PackageKit-gtk3-module

Installed Packages
Name : PackageKit-gtk3-module
Version : 1.1.12
Release : 4.el8
Architecture : x86_64
Size : 27 k
Source : PackageKit-1.1.12-4.el8.src.rpm
Repository : @System
From repo : AppStream
Summary : Install fonts automatically using PackageKit
URL : http://www.freedesktop.org/software/PackageKit/
License : GPLv2+ and LGPLv2+
Description : The PackageKit GTK3+ module allows any Pango application to install
: fonts from configured repositories using PackageKit.