If you are trying to set the width of a widget based on content–like the width of a text string in a proportional font–it won’t work. The “Fit to Content” applies to the repeater cell, not individual widgets in that repeater cell. In other words, the “content” to which the cell is being fit is the collective dimensions of all visible widgets in that cell.
In a widget’s Style pane you can click a button to Fit to Width or Fit to Height based on the text value. However, this applies only to the default text value and not to ongoing–dynamic–text value. This applies whether a widget is in a repeater or not.
Years ago I posted this example with a few different methods to dynamically resize a text widget in a repeater:
This recent post from @Jorkin describes a method to change the width of a widget programmatically based on text content. I haven’t tried it out yet but looks promising.