If it's about legato or retrigger, then you find the RETRIG TRIGGER MODE as the second switch under the GLOBAL TUNE.
Arturias ARP 2600 RETRIG TRIGGER MODE perhaps should have the label LEGATO MODE or shift the ON to OFF as you have legato mode when you have this switch on, and retrigger when it's set to OFF. (Or better use the terms Single and Multiple trigger mode from the original hardware keyboard that had this option, as the oldest perhaps only had legato trigger mode.)
But i don't know if the retrigger is working correct, as the hold note does'nt retrigger on release off a lower note, when holding a key down and then hit and release a lower note.
Like on the original, then Arturias ARP 2600 retrigger mode don't retrigger the AR envelope.
If your question is about playmode, then Arturias ARP 2600 has low note priority, meaning there is no sound if you play a higher key while having a lower key hold - like when playing legato upwards.
(There are this request for more playmodes
https://forum.arturia.com/index.php?topic=87969.0)
I believe the original hardware ARP 2600 actually had high note priority while the Minimoog had low key priority.
Also it looks like there where some speciel things about the keytrigger in the original hardware keyboard with this options.
This is from the ARP 2600 book "FUNDAMENTALS OF MUSIC TECHNOLOGY":
"One interesting trick that can be done in multiple mode is to play and hold a key, and then tap lower
keys. While the lower keys won’t sound, the keyboard will still put out trigger pulses, which can in turn
reopen the filter or VCA. This is a wonderful feature which is available only on a precious few modern
synthesizers."
Arturias retrigger version don't seem to work quite like the original. It would be nice if it could - including the Portamento trick.
And it would be good if the playmodes in the link above was added too.
