Long story short, Pandas ExcelWriter Save method got deprecated with version 1.5 released last september (19/09/22, to be precise) (here the changes about ExcelWriter).

The issue⌗

Being depecrated, the save method now raises a FutureWarning when accessed:

FutureWarning: save is not part of the public API, usage can give in unexpected results and will be removed in a future version; pandas.ExcelWriter.save() is deprecated

and it will be removed in a future version :((

The solution⌗

Use the pandas.ExcelWriter.close method - as simple as that.