There is a couple of ways to equalise columns. It depends on the functionality you need as to which method you use.
This will equalise columns
With the Equalise switch active in the Design settings the column rows need to be coloured NOT the module.
Flick the switch in the Row settings
Design > Sizing > Equalize Columns Heights
This will make the modules inside columns
Do everything as above, so flick the Equalise switch AND add the following code to each of the Row Column Main Element areas.
display: flex
There is a more detailed tutorial on how to make columns equal here
Why equalising columns in Divi is useful
Maintaining equal column heights in Divi rows ensures a clean, balanced layout, enhancing the visual structure of your website. Without this consistency, columns with different content lengths may appear uneven, negatively affecting readability, design, and user experience.
To achieve this balance, enable the “Equalise Column Heights” option within the row settings. This forces columns to maintain the same height, regardless of their individual content, resulting in a more polished and cohesive appearance.
This feature is particularly useful for product displays, pricing tables, portfolio showcases, and service comparisons. A well-structured layout improves navigation, helping visitors browse content more easily. By keeping columns visually aligned and reducing clutter, your website creates a smoother, more professional experience that encourages engagement and leaves a lasting positive impression on users.