Summary

If you click the subplot parameters window twice on macosx I get a hardware failure instruction:

python[73461:18056878] *** Assertion failure in -[View dealloc], /AppleInternal/BuildRoot/Library/Caches/com.apple.xbs/Sources/AppKit/AppKit-1894.60.105/AppKit.subproj/NSView.m:1682
[1]    73461 illegal hardware instruction

On qt5agg, the original window closes, and a new subplot parameter window is opened.

With the update in #21663, the hardware failure instruction goes away, but now a new window is opened every time.

Proposed fix

For macosx, we should probably close the subplots parameters window and create a new one to be consistent with the qt5agg backend.