Is my car battery dying?

Maybe but probably not.
Get it tested.

BUT.....I don't see any place in that picture that it says "READY".
That might mean that your foot wasn't firmly on the brake.......or you pushed the button a few milliseconds before pressing the brake.

 

That is NOT the battery voltage.
It is the charging voltage and indicates that the car WAS in the "ready" mode when you took that reading.
It tells you NOTHING about the battery itself.

 

if it's original, just replace it

 

Time to read codes

 

Advance Auto parts doesn't have licensed mechanics. You're trusting the opinion of a kid who needed a job. Load test the battery yourself

 

This is the best battery load tester. Do not buy fancy technical ones that check resistance

 

14.75 volts is most likely with the car on, so it says little about the battery. It speaks to the Inverter's DC to DC converter

The voltage when the car has been off for at least 8 hours would be of interest.

 

Lots of places said that even on batteries that were not fine. So don't take it as a final answer.

Pop the hood so that you can read the voltage at the under-hood jump point tomorrow morning without opening the driver door, which triggers some brake booster activity. Then as Jimbo suggested, measure the battery voltage after the whole thing has rested overnight, or 8 hours, without being started. That measurement will be more useful, though unfortunately still not absolutely definitive as it isn't a load test.

 

Verify the brake lights work. Then it is s time to forget about the 12v battery and start reading codes.

 

Might want to verify the brake switch is working, required to achieve Ready mode.

Autosupplies have free scans but they are usually too generic for a hybrid issue. Toyota's Techstream is the best, some like the xtool d8, others try to get by with the Dr Prius app and a bluetooth scanner. Considering the best scanners are $699 and above (unless you get an illegal copy of techstream which still needs a hardware interface); considering there is a learning curve to using the tool and diagnosing the problem; and considering intermittent electrical problems are particularly tricky even for the experienced, most go to the dealer and at least get their diagnosis.

Bluetooth Obd2
https://bit.ly/ObdTwo

Xtool D8
https://www.amazon.com/XTOOL-Diagnostic-Diagnostics-Bi-Directional-Programming/dp/B098L7ZD4K/ref=sr_1_1_sspa?crid=35AO19CB30ECW&keywords=xtool+d8&qid=1644844015&sprefix=Xtool,aps,162&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExME1DQlVaR0FaWVZRJmVuY3J5cHRlZElkPUEwODc2MzAyMVlTVFJLQ1lQNFE5RCZlbmNyeXB0ZWRBZElkPUEwMDk2OTQ0MzhQSVMzT1hQNVpUSCZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

 

This.
AND.....be absolutely sure that your foot is firmly on the brake BEFORE you push the "start" button.
Every time mine won't start it is because my finger hits the button before my foot pushes the brake pedal.
And I think that pushing the brake causes something extra to light up on the dash.