2007 ICE won't start, Red triangle, numerous codes

Long story short... was given a 2007 Prius that was very erratic and flaky. would drive fine then all dash lights come on and either limp home with revving engine or totally dead. 12v batt disconnect would set everything right until next mishap, either days or weeks. now the ICE won't start and kicks out of READY mode when it seems it would call for the ICE to start, like when AC is turned on. the back story: this car had the seam leaks, was wet with standing water in the back end under the carpets. i've done the following:
- repair leaks of course
- removed traction battery, cleaned all buss bars, cycled 6 cells on drone charger that were ~6.5v
- cleaned every connection in battery, checked for burned pins and dendrite growth on batt ECU
- cleaned batt fan, repaired corroded plug
- 12v battery new 2023 and load tests good
- cleaned ECU connectors with DeOxit D5
- tested and cleaned all fuses
- replaced relay block B with spare, cleaned pins both blocks
- substituted Network, Battery, HV, and Engine control ECUs with different

Techstream output shows these immediate codes upon clearing codes:
Hybrid Control > P3000 > Detail code 3 > 123
> U0100 > Detail code 1 > 211
> Detail code 2 > 530
HV Battery > U0100

i'm at my wits end with this car. when it was running, the traction battery tested good with the Dr Prius app, even before cleaning the terminals and rejuvenating cells. mpg was good,

as it stands now, a 12v disconnect will reset things long enough to go into READY. the car can be shuttled back and forth in EV but as soon as what seems would be the ICE start, READY goes off and car is unable to move until another 12v disconnect reset.

feel free to ask questions and lead me down to info you might need to help diagnose this.

-dan
Bemidji MN