Camunda create engine scripts broken since Oracle 12 or earlier?

Dear all,

given my issue described in Issue with DB-Update-Scripts in 7.13 (and the proposed “manual” solution), I wanted to double check my result, that is, in addition to updating the existing schema creating the schema from scratch and comparing both schemas.
When executing the create-engine script from 7.13 on Oracle 19c I got an ORA-02158 (invalid create index). Inspection shows, this is from the statement

   (case when GROUP_ID_ is null then null else TYPE_ end,
    case when GROUP_ID_ is null then null else RESOURCE_TYPE_ end,
    case when GROUP_ID_ is null then null else RESOURCE_ID_ end,
    case when GROUP_ID_ is null then null else GROUP_ID_ end);

Doing some quick search reveals this question on Stackoverflow: sql - Constraining a database table so only one row can have a particular value in a column - Stack Overflow

This makes me think that creating a camunda schema on Oracle might be broken for 5 years or more. I did some quick check on an Ora12c where the statement is also not executing with an ORA-02158.

Any ideas?
Kind regards,

PS.: While you are at it, within the oracle-update script 7.9 to 7.10 there is a bug. ACT_GE_BYTEARRAY(ROOT_PROC_INST_ID) is added with varchar(64) instead of NVARCHAR2(64) (like it is in the create script and like anyone else referencing the PROC_INST)