Caché/IRIS already has ready-made macros:
$$$FormatText(),
$$$FormatTextHTML(),
$$$FormatTextJS()

, which may be useful to you and which use #def1arg.

ISO/IEC 19075-6:2021 (see Chapter 6.4)

Wow!

By the way, if you remove the second brackets, the query works:

SELECT 1 WHERE ('') = '_㉸^'

It requires Java 17, and InterSystems IRIS Enterprise (it uses many connections).

Do I understand correctly that with the built-in Community Edition license, the SQLancer tool cannot be fully used?