How to rename all specific filetypes of files within subfolders to name with same file extension but same file name

The "newer" pathlib module is helpful here.

A recursive glob can match all filenames by extension.

>>> from pathlib import Path
>>> for p in Path().rglob('*.iso'):
...     print(p)
a/b/2.iso
a/b/c/d/3.iso
a/b/c/d/e/1.iso

The part before the extension is called the stem in pathlib terminology - you can modify this using .with_stem()

>>> for p in Path().rglob('*.iso'):
...     print(p.with_stem('game'))
a/b/game.iso
a/b/c/d/game.iso
a/b/c/d/e/game.iso

You can pass this directly to the .rename() method

for p in Path().rglob('*.iso'):
    p.rename(p.with_stem('game'))

Which will rename all of the files:

>>> for p in Path().rglob('*.iso'):
...     print(p)
a/b/game.iso
a/b/c/d/game.iso
a/b/c/d/e/game.iso