They are both made up but what is the fahrenheit? Where does the scale start? How much does it increment by? How does it relate to other units?

0F is the same, but for brine. 100F was what was believed to be body temperature (still, close enough).

This is arbitrary yes, but the importance is not if it’s arbitrary but that it is a description of a physical property in our world that can be experimentally repeated, tested and verified.

They both can. Notably, the definitions that you and I both gave aren’t actually how they’re defined anymore. They’re both defined using Kelvin, because that’s the one that’s actually more valid. C and F are just defined as points on that scale. An authority literally did decide it’s a different value than years before, as the pressure at sea level is somewhat variable. They decided to use universal constants, that K is defined with, to define both of these scales.

There’s a reason that all imperial units are scientifically described by their relation to their metric counterpart and it’s because metric units are based on physical properties of the universe around us and so we can measure them as opposed to just define them.

See above. You’re thinking of SI units, not metric. They’re mostly the same, except notably the SI unit for temperature is Kelvin, not Celsius.