df = df.applymap(lambda x: x.strip() if isinstance(x, str) else x)
print (df)
                     A    B     C
0                  A b    2   3.0
1                  NaN    2   3.0
2               random   43   4.0
3  any txt is possible  2 1  22.0
4                        23  99.0
5                 help   23   NaN