Front Massage & Rear Ventilated seats

[IMAY2023]

The seats are totally different. The massage ones have air bladders built in that inflate/deflate to create the massage effect. Similar to the ventilation -- there's an audible fan you hear kick on (rather loud) when you turn that feature on.

This makes sense, but I'm wondering about XC90 Inscriptions w/ ventilated seats. I enabled massage seats in config but the option doesn't appear in the IHU. Anyone done this yet?

You cannot just activate the massage seats and expect it to work. 
I did full upgrade of seats, I retro fitted S90 (Massage, heated and Vent Front seats, and heated & Vent. rear seats) to my 2019 S60 Momentum (used to be :-) ) that had only front heated seats. 
So, massage seats are totally different and it has nothing to do with Heated & ventilated elements and controllers. Massage seats have their own controller and power wire from fuse box.
For the rear seats (adding heated and ventilated) is completely different story. Requires whole bunch of wiring.  

Even if you get and replace your (heated & ventilated ) seats with  (heated & ventilated & massage & side support) and then activate from Orbit, still it won't work. Because you have a missing power wire. From PIN 15 of each seat connector to the fuse box with 7.5 AMP fuse. Both seats (PIN15) are connected to the same fuse.