Never worked with text from KNX to HA, but you could test it yourself using ETS.
If you do not have ETS, there is a demo version if you register which allows 5 devices, but you can create the group and send a text telegram on the diagnostics page without needing an actual device in it.
Then I guess you are looking for a sensor, not a text entity. A text is a bidirectional entity - you can send a new state… but an error code should only be sent from the device having the error, doesn’t it? respond_to_read: true also doesn’t really make sense to me here for the same reason.