Take data from one column into Dropdown Multi-Select

I have a column populated by a Form that contains list data. For example, the options in the form could be "Yellow", "Green", "Blue".

Depending on the selection in the Form by the user, the content of the column could be any combination of the options. Where multiple options are selected it would display them as a string - e.g. "Yellow, Green, Blue" or "Yellow, Blue".

I want to have a corresponding Dropdown Multi-Select column that will mirror the column data but will store it in the neat Dropdown Multi-Select way (for reporting purposes).

I'm guessing I need one or more 'helper' columns to strip away the punctuation and then a way to combine them correctly so they are displayable in the Dropdown Multi-Select column type.🤔

*Unfortunately I cannot use Smartsheet Forms as part of my process so I cannot simply use the Multi-Select Question field to populate the column*