So about DB2:

• the driver is obfuscated and not helpful
• the feature is apparently not supported even if they claim they support JDBC 4.0
• there's no literature on the Internet
• the exception is very clear and the behavior is very clear too: it simply does not work so there's no tricky behavior for the end user
  -> my vote would be to not run the test on DB2.

About Sybase, I found this https://wiki.ispirer.com/sqlways/sybase/data-types/unitext , apparently, it's the type we should use as a nclob replacement.

HTH