One of the new features the modern SharePoint interface now provides is the ability to adjust the width of columns. As you would in a spreadsheet, locate the boundary of a column, click, drag and re-size to the desire width.
You can from the above, that I have re-sized the initial column width of the above Document Library.
Unfortunately, from what I can see, that changed column width doesn’t remain if you navigate away from the page. Thus, if you go somewhere else in your Team Site and then return to the original location the column widths are back to the way they were initially.
Hopefully Microsoft will soon add the ability for ‘re-sized’ columns widths to ‘stick’ after any change. However, having the ability to easily adjust column width in SharePoint is great additional functionality that has been missing for a long while.