Code P0300?

No, those are normal oxygen sensor voltage readings, what is your MAF reading at idle? Also clamp off the block off the brake booster hose completely, so the booster is out of the equation and see what the fuel trims do. The reason the fuel trims changed after warming up is because when the vehicle is in Open Loop during its warmup to operating temperature, the ECM doesn't use the Oxygen sensor data to calculate its fuel strategy. Once the engine goes into Closed Loop operation, it then uses the Oxygen sensor data and it's still seeing a lean exhaust and adjusting for it. Start to block off some hoses that go to the intake manifold one at a time and see which one causes the short term to come down. Now if your Long term fuel trims are high, for example lets say Long Term is at 20%, and you find a vacuum leak, block it off, now since the Long Term is at 20% (and Long Term is more of a learned value), you will see your short term go to -20%. To correct for the already learned value of the Long Term, when you add 20% and -20% you get 0%. Does that make sense? Once the problem is corrected, the Long Term will eventually learn the correct Fuel trims, and everything will even out.
So, block off the booster hose, unplug the Purge valve and block it off. Any vacuum lines one by one until you find the issue. Or do a smoke test on the booster and intake manifold. There's still a leak somewhere. Can you graph both front oxygen sensors for me after it has warmed up so I can see the waveform?

Can you show me the graphs for the 2 front Oxygen sensor graphed voltages only, not the fuel trims, so oxygen sensor Bank 1 Sensor 1 voltage, and oxygen sensor Bank 2 Sensor 1 voltage after warming up when you notice this drop to 0 volts. And on the graph show the point at where they drop and go to from 0.8volts to 0volts. I know your scan tool may read Oxygen sensor STFT %, but I need to see the voltage readings. And in a separate picture the live engine data after warming up at idle. I can't tell what's happening unless I can see what the ECM is seeing.

That scan data is extremely slow, those Oxygen sensors are fluctuating much faster than what you are seeing on that screen. Yes, the purge valve can cause a lean condition, if its sticking open, once it's purged all the vapors out of the canister it will be pulling straight oxygen threw the canister vent valve which is normally open. If the canister failed and the charcoal pieces broke apart, they get stuck in the purge valve and keep it open. Try unhooking one of the lines to it and blocking it off. There seems to be sections of the oxygen sensors that are hanging both rich and lean, the upper one on the screen was much slower. But cylinder misfires can cause that as well. When a cylinder misfires, raw fuel and oxygen go down the exhaust, and since an oxygen sensor can only read oxygen, it can send the system rich, just increasing the issue.
If you don't find any more vacuum leaks, then start thinking about clogged injectors, fuel filter, weak fuel pump, bad fuel pressure regulator. All those faults will cause the ECM to enrich the mixture due to a lack of fuel. Your fuel trim numbers are very high, pretty much at the max level.
To check the fuel injectors you'll have to get a fuel injector pulse tool, with a fuel pressure gauge on the rail, you get the pressure up to its max, then pulse each injector one at a time and write down how much the pressure drops, Check the purge valve first, make sure it's not stuck open, or drawing in air from a broken Evap hose.

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

I'm so glad you found the fault, was the purge valve stuck open? You should tap the Purge valve in the ground and see if any charcoal pieces come out, if anything falls out of the valve that means the Canister is most likely at fault, and the charcoal inside has broken up and traveled into the purge valve preventing it from closing all the way. The same thing will happen to the new purge valve if the charcoal canister has failed. The reason they go bad is because of over filling the gas tank, The fill handles at the gas station are design to click off when the tank is at the correct fill level, Some people will pull the handle out a little further to try to get more gas in the tank, but this is what causes gas to get into the canister and ruin the charcoal, So just be aware of that.
I believe we do take donations; they go to making repair videos for our YouTube site, they do not go to the technicians. I will get the link for donations and post it here if you want to make one to the site.

Okay, sorry for the wait. I had to get the link for donations to the site. And about the purge valve, I don't know if it's the same type of design, but I had a case here where the owner of the vehicle put the purge valve on backwards, I guess the vapor line coming in and going out to the intake were exactly the same, and he had them hooked up backwards, that was a fun week. Apparently, the valve will open on its own by manifold vacuum if hooked up backwards. The ECM was setting circuit codes because on its self-tests it wasn't seeing any voltage on the control wire at idle because the valve was already open. I couldn't believe it, that it was a Chevy Aveo, I know you've worked on vehicles a long time, but I thought it was an interesting story since you happen to be changing that valve.

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