Mmm, I'm not sure what the idea here is.
Let's start with the basics.
In a Spice simulation it will try to make sense of whatever you give it, even if values are so far out of where its models work.
An 80 M resistor connected to a 0.01 ohm resistor?
For scale, that's like the difference between a 50,000 ton ship and a sheet of note paper.
Yes, there are 100 M resistors, but they are usually for high voltage probes.
Moreover, if you breathed heavily on the circuit you can probably make a 100 M short circuit yourself.
High side current measurement has to be differential across the shunt resistor.
You have to measure both sides and take the difference.
Texas Instruments makes tons of chips, both analog and digital that do a good job of this.
I'm mostly familiar with the digital ones, INA219, INA226.
Here's an analog one:
https://www.ti.com/product/INA169Yes, you can make your own circuit from scratch.
The tricky part is to make the parts matched well enough that having the average voltage of the two points of the shunt not affect the current measurement.
That's the common mode rejection ratio.
Edit: Ah, I see, that SLAU502 is a voltage to current converter, not a current measurement circuit.
Did you mean more like this?
https://www.ti.com/lit/pdf/sboa310