On Fedora 35, I still reproduce the initial issue on the main branch of Python:

$ ./python -E -m test -v test_readline test_builtin
(...)

======================================================================
FAIL: test_input_tty_non_ascii (test.test_builtin.PtyTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/vstinner/python/main/Lib/test/test_builtin.py", line 2095, in test_input_tty_non_ascii
    self.check_input_tty("prompté", b"quux\xe9", "utf-8")
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vstinner/python/main/Lib/test/test_builtin.py", line 2086, in check_input_tty
    self.assertEqual(input_result, expected)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 'quux' != 'quux\udce9'
- quux
+ quux\udce9
?     +


======================================================================
FAIL: test_input_tty_non_ascii_unicode_errors (test.test_builtin.PtyTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/vstinner/python/main/Lib/test/test_builtin.py", line 2099, in test_input_tty_non_ascii_unicode_errors
    self.check_input_tty("prompté", b"quux\xe9", "ascii")
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/vstinner/python/main/Lib/test/test_builtin.py", line 2086, in check_input_tty
    self.assertEqual(input_result, expected)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 'quux' != 'quux\udce9'
- quux
+ quux\udce9
?     +
(...)


Fedora 35 uses readline 8.1:

$ ldd $(./python -c 'import readline; print(readline.__file__)')
	...
	libreadline.so.8 => /lib64/libreadline.so.8 (0x00007fd00e553000)
	...
$ rpm -qf /lib64/libreadline.so.8
readline-8.1-3.fc35.x86_64

$ make pythoninfo|grep readline
readline._READLINE_LIBRARY_VERSION: 8.1
readline._READLINE_RUNTIME_VERSION: 0x801
readline._READLINE_VERSION: 0x801