It is because of duplicate of hsqldb.jar in installer classpath.
Workaround:
1. Run installer as normal
2. Right before config RDBMS steps.
Database Management System Configuration
Use an already installed DBMS [1, Enter]
1
Select DBMS for metadata:
MariaDB [1, Enter]
MySQL [2]
3. Delete hsqldb.jar in temporary extracted installer dir (in my case: /home/apps/Knowage-7_2_0-CE-Installer-Unix-20200730.sh.14611.dir)
rm /home/apps/Knowage-7_2_0-CE-Installer-Unix-20200730.sh.14611.dir/user/hsqldb.jar
4. Continue installation