Yes, I have the 'old' 3.9.5.  In IDLE, ^C does not break the hang, but Restart Shell does.  As I expected, I had to skip test_outwin's test_write and test_writelines to stop that test hanging.

Next failure: test_sidebar.LineNumbersTest ends with test_toggle_linenumbering ... OK.  That is the last test method and the hang is in tearDownClass "cls.root.update()".  Changing to .update_idletasks() fixes this.  I believe that the latter is what we usually use before destroying root.  But still, update should not crash.  At worst, a TclError.

With this fix, test_idle passes.  So do test_tcl and test_ttk_textonly.  Test_tk and test_ttk_guionly each have 1 failure.  (For me) The test suite as a whole is a mess, with multiple Python-crashed message boxes.