A geometry Sector Solver, Value finder for my calculator's micropython
Naming

Variable and function names should be snake_case, not This_Format or This. Uppercase and PascalCase are reserved for class names.

Checking inside lists vs strings

If you're checking for a single character, it's better to use a string rather than a list. Have a look:

if unit in "+-":
    ...


The walrus operator

If you're using python-3.8 you can use the walrus operator. It's another way of saying assignment expressions. It's a way to assign a variable within an expression. In your case, you can utilize the walrus operator to assign input to a variable, and use that. Have a look:

while unit := input("For Degrees, enter '+',\nFor Radians, enter '-'\n: "):
    if unit in "+-":
        ...


So unit is assigned whatever the output of the input  call is.

Unneeded function

If your function is simply an input call, you don't really need it. Just put it at the end of the while loop.

Ternary operators

You can use these to greatly shorten the length of your code. It's an easier way to assign values based on conditions. Take a look at the final code to see what I'm saying.

f-strings

You should use f"" to directly implement variables in your strings. It's a cool feature that keeps you from having to + or call a .format on your strings. Have a look:

print(f"Area of Sector = {sector_area}")
print(f"Area of inner Triangle = {triangle_area}")
...


Final code

After all these suggestions, you code would look something like this:

from math import pi, sin

def input_pi_replacer(prompt):
    return float(eval(input(prompt).replace("pi", str(pi))))

print("Sector Quantities Calculator:\n")
while True:

    while unit := input("For Degrees, enter '+',\nFor Radians, enter '-'\n: "):
        if unit in "+-.":
            if unit == ".":
                raise SystemExit
            c_factor = (pi / 180) if unit == "+" else (180 / pi)
            break

    radians = input_pi_replacer("\nEnter Radius: ")
    angle = input_pi_replacer("Enter Theta/Angle: ")

    c_angle = angle * c_factor if unit == "+" else angle

    print()
    sector_area = 1 / 2 * (radians ** 2) * c_angle
    triangle_area = 1 / 2 * (radians ** 2) * sin(c_angle)
    arc_length = radians * c_angle
    chord_area = sector_area - triangle_area
    chord_length = 2 * radians * sin(c_angle / 2)
    perimeter_sector = 2 * radians + triangle_area

    print(f"Area of Sector = {sector_area}")
    print(f"Area of inner Triangle = {triangle_area}")
    print(f"Arc Length = {arc_length}")
    print(f"Chord Area = {chord_area}")
    print(f"Chord Length = {chord_length}")
    print(f"Sector Perimeter = {perimeter_sector}")
    print()

    if input("Stop?: ").lower() == "x":
        raise SystemExit