How do I make many labels for the current length of the Text in a tkinter Text widgets

When update() is executed, the value of i will be the last assigned value after the for loop, i.e. 10.

You need to capture the required value of i and pass this value to update() using argument default value:

for i in range(1, 11):
    def update(event, i=i):
        label_all[i-1].config(text="Total Characters: "+str(len(text_all[i-1].get("1.0", 'end-1c'))))

    ...

Also you can merge the two for loops into one:

for i in range(1,11):
    def update(event, i=i):
        label_all[i-1].config(text="Total Characters: "+str(len(text_all[i-1].get("1.0", 'end-1c'))))

    text=Text(win, width=20, height=1, font=('Calibri 14'))
    text.grid(row=i-1,column=0)
    text.bind('<KeyPress>', update)
    text.bind('<KeyRelease>', update)
    text_all.append(text)

    label=Label(win, text="Total Characters", justify=CENTER, font=('11'))
    label.grid(row=i-1, column=1)
    label_all.append(label)

All I had to do to get your code working was to remove the geometry statement in order to allow Text to determine window size and change update(event) to update(event, i = i):

Everything else works as is!

from tkinter import *

win=Tk()
# remove and let text widget determine width of window

# win.geometry("700x350")

text_all=[]
label_all=[]
for i in range(1,11):
    text=Text(win, width = 40, height=1, font=('Calibri 14'))
    text.grid(row=i-1,column=0, sticky=EW)
    text_all.append(text)
    label=Label(win, text="Total Characters", justify=CENTER, font=('11'))
    label.grid(row=i-1, column=1, sticky=EW)
    label_all.append(label)

for i in range(1,11):
    def update(event, i = i):
        label_all[i-1].config(text="Total Characters: "+str(len(text_all[i-1].get("1.0", 'end-1c'))))
    
    text_all[i-1].bind('<KeyPress>', update)
    text_all[i-1].bind('<KeyRelease>', update)

win.mainloop()