Hybrid battery or 12v?

I am trying to sell my 2008 and have been traveling near-constantly for months so it's been sitting in my driveway far too long and driven far too infrequently. I had to jump the 12v a while back and it started up and drove as normal. A few weeks ago, I tried to take it out for a drive and needed to jump the 12v again. After the jump, I haven't been able to drive it. Power locks work, proximity key works, and it starts up seemingly normally, with the AC and radio kicking on, but when I try to shift it into drive, it goes into neutral and won't move. The screen says "PROBLEM" and "MAIN" with a battery +/- symbol. My OBD scanner showed the P3000 code and that the battery cells were all green except for a single red one (but I've driven with a dead cell in the past with minimal issue).

The battery jumper I used was malfunctioning, and I forgot to get the OBD read of the 12v, so there's a chance it's still low. But the hybrid battery has been dying for awhile now, and even when it drove, the dashboard lit up like a Christmas tree. I'm not sure if the 12v is still too low to start the car fully, or if the hybrid battery is officially dead. If anyone can give me pointers on making the determination, please let me know what I can check or how I can get it started again.

Thank you in advance!