Alright I decided to open the inverter to see what I could do with the temp sensor.
The terminals for the AC outlets of the inverter are super loose, they popped out of their place when I removed the front cover of the inverter.
Also the N and L cables are flipped around, the PCB says that the black cable is neutral and red is live, while they are backwards in the 3 outlets, now that really isn't a problem because this inverter is fully isolated from the DC side and behaves more like an isolation transformer.
The ground terminals are connected to nothing, again not a problem because of how the inverter is built, normally at the very least these should connect to the metal case of the inverter, but this inverter is built like a double insulated PSU, there's a insulation layer on the underside of the PCB even.
The inverter is easy to open, the fans have their own connectors each, I just had to disconnect each fan and also disconnect the cable for the display and the PCB was out.
There are two NTC termistors as temp sensors, both are read by the display which is surprising (Thought that one would feed into the display and the other would just be a overtemp protection that would shut the inverter off), the one that has the decalibration issue is the NTC for the AC side of the inverter, if removed the temperature display displays the temperature of the DC side NTC which at 88F ambient temperature reads 93F, not too far off.
Here is a video showing the temperature display with the AC side NTC (shows the temp of the DC side NTC instead), then with the AC side NTC connected (shows 99F) and finally with a 3K resistor in series with the NTC, which just drops the temperature from 99 to 97F, a higher value resistor will reduce it even further, however doing so will disable the NTC because the resistor doesn't lower its resistance by increasing the temperature, so lets say that at 50C the NTC drops to 5K Ohm, if I added a 4.7K resistor instead the AC side would not be able to read temperature above 50C.
Since I don't have other NTC what I just did was add a 3K Ohm resistor in series with the NTC, this isn't ideal however I tested to check if the fans turn on and they do, this really didn't fully fix the inverter, every 4 minutes it will still turn the fans on for about 2 minutes when idling, I will need to replace the termistor with one of a slightly higher value.
Vid after being partially fixed:
Also I tested the idle power draw, with fans off it is 9.59W and with the fans on it is 16.1W, the display reads 20W+ in both cases.
More pics of the insides: