Weird, I've been able to download the STM32CubeIDE Generic Linux Installer without troubles. This is actually my preferred one since it is the only installation procedure allowing self-update application. Other installation modes will stay on a fixed version. There are pros and cons to this depending on your needs.
The installation guide is under Resources / User Manuals / UM2563.
Once zip downloaded and extracted you get a .sh script file.
Make it executable (chmod +x ***.sh) and launch it from a terminal.
For Ubuntu, either:
sudo ./st-stm32cubeide_1.4.0_7511_20200720_0928_amd64.deb_bundle.sh
or
./st-stm32cubeide_1.4.0_7511_20200720_0928_amd64.sh
The 2nd will ask you later to execute some install steps as sudo. This is required since STLink-Server, Udev rules for STLink/Jlink installation need to change some basic system settings.
HTH :)
To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.