The icon is new to me, started showing up when version 2022-40.4.1 uploaded a couple days ago. It has been coming on here in Utah, since temperatures have been cold below 27f (-2.8c). Prior to the update, a full "Regen is limited" banner appeared under the onscreen car and stayed on for many miles (35) until the battery gets warmed up. Tonight, it was 27f and the icon stayed on the whole trip.
If I press on the green regen icon, it opens a full explanation banner below.
I've definitely noticed limited (practically no deceleration) quite often when the green icon is on (regen works intermittently, not totally broke). The car just coasts with very little slowing. I'm glad the icon is showing onscreen, as it has been a bit unsettling when approaching a stop light, and the car is coasting as if it will run right through the light, needing to press the brake pedal. I've just enabled using actual brakes during this condition, not sure if it will be a better experience.