Dont think of the cable as the equivalent of a resistor. (It is but needs different considerations)
A cable of a certain cross sectional area is designed to carry a certain amount of current. Because of the resistance of a cable it will generate heat. A fatter cable generates less heat than a thin cable. All cables (except say overhead cables) are covered with an insulating material. Heat up the cable too much (too many amps) and the insulation will deteriorate, either gradually or spontaneously. The cable manufacturer will tell you how many amps the cable can carry so as not to degrade the insulation. That rating also depends on where and how the able is mounted.
The other consideration is what voltage drop will your length of cable have. The cable manufacturer will provide the cable resistance (per length) and by ohms law you can calculate the voltage drop. In power systems its usual to use a 3-5% voltage drop. Voltage drop is not a bit consideration is the cable is not more than some tens of meters.
Engineers and electricians can quickly work all the above out. But companies like Victron are selling their products to non techies. So they develop these calculators for non techies. The inputs are very general and the putputs are very conservative. Youll find the result will always work but is not the optimal result.
How much power does the cable use? In transmission theory the "power" of the cable is the received amps times the received volts. Since the cale does not know the volts, a cable can carry tremendous amounts of power if the voltage is high.
How much power does the cable use (or burn up as heat)? The difference in voltage between the start and the end of the cable times the amps its carrying.

 

This is a useful calculator
https://www.solar-wind.co.uk/info/dc-cable-wire-sizing-tool-low-voltage-drop-calculator
As it tells you both the loss, and whether is it safe, and also gives diameter and minimum bend radii

 

This is a useful calculator
https://www.solar-wind.co.uk/info/dc-cable-wire-sizing-tool-low-voltage-drop-calculator
As it tells you both the loss, and whether is it safe, and also gives diameter and minimum bend radii

Like I said in my earlier post, these online calculators are very conservative. I tested a few scenarios and determined the cable size was 3-4 times larger than necessary.

 

Like I said in my earlier post, these online calculators are very conservative. I tested a few scenarios and determined the cable size was 3-4 times larger than necessary.

On the contrary, it appears to be completely aligned with the wiring regulations. if I enter 160A it says "caution" for 50mm^2 cable and the regs say that 50mm^2 is acceptable for a pair of cables (but no more than 2) clipped direct to a wall, but not in conduit or thermal insulation.

 

Why would a calculator be based on 3% drop, because that’s what code allows.

 

Like I said in my earlier post, these online calculators are very conservative. I tested a few scenarios and determined the cable size was 3-4 times larger than necessary.

Indeed I just tried it with the same values as I did with the Victron calculator and I got recommended a solar cable gauge of 16mm2 for 15A.
This, and considering a cable as a resistor, are really what originally threw me off. To me total power was the decisive factor in selecting a cable that was big enough to dissipate the heat and I couldn't understand how the calculator would recommend a smaller gauge for higher voltage but same amps which equals higher power. Some people here believed that I didn't understand that for equal power, amps go down as voltage goes up, but here we are talking about power generation and putting panels in series will conserve the amps while increasing the voltage.
I know now that calculators advise for voltage drop, and that cables are rated for amps (and insulations for breakdown voltage and resistance to heat). The higher the voltage, the smaller the percentage for the same cable voltage drop hence the seemingly paradoxical result. @kaindub your post is spot on, but the mental gymnastics I went through during this whole thread was probably necessary for me to understand why a cable shouldn't be treated as a resistor.
Thanks again to everyone for helping out.