You shouldn’t be using Audacity 2.3.0 on Linux. The 2.3.0 release is for Windows and Mac only. The latest release for Linux is Audacity 2.2.2 https://www.audacityteam.org/download/linux/
Audacity 2.3.1 is scheduled for release next month, but until then you should use Audacity 2.2.2 or earlier.
Note that it is highly recommended to use software packages provided by your Linux distribution as these should have been tested for compatibility with the operating system.
The official release version of Audacity for Ubuntu 18.04 is Audacity 2.2.1-1 (https://packages.ubuntu.com/bionic/audacity), though please be aware that there is a bug in this version that you will need to work around: When saving a project that has previously been saved, use the “Save” command (or “Ctrl+S”) and NOT the “Save As” command. Overwriting a project with “Save As” will corrupt the project. Overwriting the previously saved project with “Save” works correctly.