There is currently a bug affecting the RebornOS Welcome application, due to which the application may not launch. This bug does not affect all users and it is perhaps not reproducible. To fix it, you would simply have to run the below command on a terminal:
rm -f ~/.rebornos-welcome/configuration/settings.json
Technical details: The local configuration file settings.json sometimes gets corrupted with junk characters at the end. Deleting the file using the above command will let the Welcome application recreate it correctly.