Control groups and experimental groups are exactly the same except for the

Control and experimental groups are alike in every respect except the independent variable applied to them.

Only the experimental group receives the treatment level of that independent variable.

The dependent variable is measured as the outcome, not the feature deliberately made different.

Extraneous variables are held constant across both groups rather than distinguishing them.

Replication variables are not a recognised category separating the two groups.

Keeping everything else equal is what lets any difference be attributed to the treatment.