Is It Possible To Expand the Display Width for Related Records?
You cannot expand the display width (field width) for Related Records.
Display width is automatically adjusted by your Web browser based on the value of the field.
For your reference, described below are the steps to add a space to a field name and adjust the display width of the field, in the app that is specified as the "Datasource App" in the Related Records Settings.
The steps are as follows.
Open the app that is specified as the "Datasource App".
Click the app setting button on the upper right of the record view, to open the form setting screen.
Place the cursor over the setting button on the upper right of the field that you want to adjust the display width, and then click Settings.
Add a full-width space (empty space) at the end of the field name to lengthen the field name, and then click Save.
You need to enter a period at the end, because without a period, added space will be truncated when the field name is displayed.
Click "Save Form" on the upper left side of the screen.
Click Update App on the upper right of the screen, and then click OK.
The display width of the Related Records field is expanded to include the added space.