How to increase the width of a SharePoint Online List column in a List WebPart


It’s not recommend to create or add ungoverned code on modern SharePoint pages, you need to get started with SPFx:

https://sharepoint.uservoice.com/forums/329214-sites-and-collaboration/suggestions/17290130-bring-back-script-editor-web-part-in-modern-shar

You could consider using json formatting as shown below to increase the width of list column:

{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/column-formatting.schema.json",
  "elmType": "div",
  "txtContent": "@currentField",
  "style": {
    "color": "green",
    "width": "300px"
  }
}

Result:

enter image description here

Reference:

https://docs.microsoft.com/en-us/sharepoint/dev/declarative-customization/column-formatting