We need some infos to help you.

- What's exactly the problem?
- Is the pump running?
- Any noise you can hear from the pump?
- If you remove the PWM cable: Does the pump spin?

your PSU does deliver 12V on the molex port (5V on one side, two grounds in the middle and 12V on the other side.
If you don't have 12V, it means either your cable is damaged, or you may be using a modular cable from another manufacturer/PSU that has a different pinout.

that cable is from a corsair PSU too?

the Peripheral + SATA connector provides ground, 3.3V(only on SATA), 5V and 12V

You need both, 12V and 5V to power the pump. Maybe you have an Voltmeter to check your cable and the PSU output if it delivers these voltages.
This should be available at any SATA port - even at Corsair PSUs.

Are you trying to run the pump without other devices connected to the PSU? This could be an issue as the consumed power is maybe too low for the PSU.

SATA delivers all 3 voltages, 3 pins for 3.3, 3 pins for 5v, 3 pins for 12V, then grounds, and one data pin. Molex lacks the 3.3V but has a higher current capability. That's why usually pumps have Molex connectors.

Regarding cables, they are not standardized on the PSU end. only the component side (molex, sata, PCIE etc..) are standardized. That would explain why you don't have 12V going to your pump.
In general, ALWAYS use cables from the PSU manufacturers, or 3rd party cables for that particular PSU model. At best you miss some voltages, at worst you can fry components.

don't know what your build is made of

the temps look alright, but they will depend mostly on your ambient temperature, fan speeds and how many rads you have, more than pump speed.
I bet if you kept a constant speed around 110 - 120 L/h you wouldn't see much difference. But at least it shows pump control works fine.

Without knowing which hardware you are cooling it is not possible to say anything about the temperatures ;-)
But there is one exception, a water temperature of over 40°C is rather high.
In such a case I would think about more radiator surface or better fans.
Again, just guessing in the blue, since the information about what you are using is not available :-)

well with just one radiator they are hot, but good :p
but you're really pushing it with a single 360mm and about 500W of heat. you could really use a second 360mm and not have to run the fans that hard.
And with PETG tubing, you don't want warm water :p

In your first set of results, you say your CPU and GPU are both at 25°C but the coolant is at 30-32°C. I don't see how this can be possible. How can the CPU and GPU temps be below coolant temp? If they were, the coolant would actually be warning them up! I also don't think a 3080TI FE is going to sit at 25°C, even at idle, no matter what's cooling it. What is the ambient room temp? Are you sure these numbers are right?

Is that flow meter a Thermaltake Pacific TF1 or TF2? If it's the TF1 you should read THIS very interesting review. I recall reading somewhere that the TF2 model is more accurate than the TF1. Did you consider an Aquacomputer HighFlow Next? They are considered to be the most accurate flow meter made for computer custom cooling loops. Also, most flow meters work better if there is a few inches of straight tubing on each side of it. Having a fitting very close to the flow meter can cause turbulence that can affect the flow meter's accuracy. Having the T fitting for your drain and that short 90° bend up to the GPU could be affecting the flow meter.

Pump Speed - The pump speed, within a wide operating range, does not significantly affect temps. Try setting your pump at 30% and do a CPU & GPU stress test. Note the CPU and GPU temps. Let it cool back down then change your pump speed to 80% and repeat the stress tests. I think you see that pushing the coolant around faster does not lower temps. Many people just pick a pump speed and flow rate that they like and leave it there. If pump noise is an issue then that may be a reason to slow it down. If it works well at that setting just leave it there. Speeding it up won't really do anything, I think running the pump at 15% and 60 - 80L/Hr is a bit low but if everything is happy and your temps are good (which they are), then I guess its OK.