Seems like the debugger output has been changed in a new ST toolchain's version.

You can fix the issue locally by changing the regex in "serverStarted" parameter in launch.json file inside .vscode directory of your project. For example, a regex that should work with both old and new versions of ST toolchains is "serverStarted": "(Waiting for debugger connection.)|(Waiting for connection on port .\.\.\.)",.

It will be set as default template in the new version of extension once it is released.

Check uprtdev Answer here