We try to not add a new parameter in a bugfix release as that can be difficult to use.  That said, adding a new bool keyword only parameter to control this behavior seems feasible.

Unfortunately you already have to deal with the existence of 3.9.5 having the new behavior but not having a control.  (maybe you resort to the global behavior change there by monkeypatching the list? removing tab is probably enough as I doubt you rely on newlines in your scenario?)

Code wanting to support versions before this patch _and pass that new parameter_ winds up needing to resort to inspect.signature(), or a call with the parameter, catch the NameError, and retry calling without it pattern.  Not unheard of.  And so long as most code doesn't ever need to do that trick, is fine.  (it can be checked for at module import time rather than doing it on every call to save overhead if that matters)

meta: Marking the issue as open while we decide if we'll be doing something here.