The IR codes for Flex are also available in the manual page 28.
Following a support request with miniDSP, they have confirmed that they are in contact with Logitech to have the IR codes added in their database.
Following a support request with Logitech, they have claimed yesterday (21 February) that Flex is already in their database and needs to be added with
Manufacturer: minidsp
Model: miniDSP FLEX
If you want to enter IR codes to Logitech Harmony which are not available from the remote control or the Logitech database:
Since IR codes cannot be entered directly to Logitech Harmony, the IR codes need to be generated by a different device so that Logitech Harmony can learn from the IR command itself. I am using an USB dongle called LearnIR which can receive and transmit IR,
https://www.analysir.com/blog/product/learnir-advanced-infrared-learner-module/ There is a web page translating the hexadecimal NEC codes into the correct format, which can then be edited in the library file of the LearnIR software,
https://www.analysir.com/hex2nec.php