Jesus was talking to his disciples. It should be obvious that nobody can perform miracles today.

Mark 16:7 wasn't part of the original book of Mark. It's not in the better manuscripts.

https://en.wikipedia.org/wiki/Mark_16#Possible_Scenarios

Textual critics have identified two distinct alternative endings: the "Longer Ending" (vv. 9-20) and the unversed "Shorter Ending" or "lost ending",[1] which appear together in six Greek manuscripts, and in dozens of Ethiopic copies. Modern versions of the New Testament generally include the Longer Ending, but place it in brackets or otherwise format it to show that it is not considered part of the original text.