One train/test split gives one opinion. Cross-validation gives several, and their spread tells you how much to trust the average.
Task: write cv_mean_and_spread(n_folds).
load_breast_cancer(return_X_y=True, as_frame=True).make_pipeline(StandardScaler(), LogisticRegression(max_iter=1000)).cross_val_score on all the rows, using cv=n_folds.Return [mean, spread]: the mean of the fold scores and their standard deviation (NumPy's .std()), each rounded to 3 decimal places.