Have you read the D5 Next Manual? Sections 11.2 and 11.3 explain how to use the Target Temp and Curve Controller modes.
The D5 Next does have a 4-pin PWM fan header that can also be configured to connect a flow sensor. I don’t think it's possible to plug a standard 9-pin USB2.0 connector into this PWM fan port, and if you somehow did, it would not work. I looked on Lion Li’s site. There is a UNI HUB controller and a UNI HUB – SL L-Connect 3 Controller. If you specified which one you have, I could look at what cables are provided with it.
This is a 9-pin USB2.0 connector: If it is wired for only 1 USB port, there are 4 wires used: 5VDC, Ground, Data (+), Data (-)
This is a 4-pin PWM Fan connector:
This is the back of the D5 Next Pump:
Click on the images to enlarge. I do not see how you could possibly plug a 9-pin USB2.0 connector into the 4-pin PWM fan header on the D5 Next. Since Aquasuite is controlling your Lion Li fans, I think you have plugged in a 4-pin PWM connector from the Lion Li controller in the D5 Next fan header, and it's working because you can control the fan speed in Power Preset Mode. To use Target Temperature or Curve Controller modes, you have to assign a temperature in Aquasuite to be used as the control source for the Target Temp or Curve Controller. The D5 Next has an internal coolant temp sensor, so it would be easy to use this as the control source. Here is a snip of the D5 Next Fan Mode section with the D5 Nest coolant temp sensor selected as the temperature control source for the Fan port in Target Temp mode.
Many people prefer to set up a Virtual Sensor in the Aquasuite Playground that is Coolant Temp minus Ambient Temp (referred to as Delta-T). Doing this, of course, requires a coolant temp sensor and an ambient temp sensor. Using CPU temp is not advisable because CPU temp jumps all over the place. I suppose you could bring the CPU temp into the Playground and use the functions there to make a Virtual Sensor that is the average CPU temp, but just using the coolant temp or Delta-T would be better choices. You have not mentioned what temps you are monitoring in Aquasuite or if you have assigned a temperature sensor as the control source for the PWM fan port on the D5 Next pump. If you have not done this, the Target Temp and Curve Controllers cannot work because they are both based on a temperature, so you must assign one.