Here are two suggested solutions:

(a) Using an assignment expression with a tuple:

>>> t = 1, 1
>>> while (t := (t[0] + t[1], t[0])) < (5000, 0):
...     continue
... 
>>> t[0]
6765

(b) With an assignment expression involving input in a while loop:

>>> while (s := input("> ").lower()) != "exit":
...     print(s)
... 
> hello
hello
> bye
bye
> quit
quit
> :q
:q
> exit
>>>