Every few times I open a particular spreadsheet I find the column sizes have changed - sometimes all of them and sometimes just some. This has just started happening in the last few weeks.
Are you saving your spreadsheets as file type .ods?
If you are saving as.csv there is no formatting stored in the file, that includes no column widths, no formula, no font size, etc.
Note that changing the extension by itself does not change the file type
Actually it is saved as an .xlsx
Try Save as [Filename]v2 and make sure in Save as Type field that you have selected Excel 2007-365 (.xlsx).
If you created the spreadsheet by right-clicking in File Explorer and selecting New > OpenDocument Spreadsheet then it is probably saved in csv format, especially if you just overtyped the extension with xlsx
In any event you can expect some issues when you save in a format that is not Open Document Format, that is .ods. Always save in .ods format and only if someone else needs a copy and cannot open the only ISO standard format, then Save as .xlsx a copy just for them.
You might like to look at Differences between Microsoft and AOO/LO files on OpenOffice forum.
Unfortunately it is not possible to set column or row widths, so the solution is, for columns to use the necessary spaces in the column to suit the desired, and character size to suit the height. So the formatting doesn’t change.
My .ods xls & xlsx spreadsheets retain the width and height settings I gave them, even if too narrow for the text or too big.
I think I expressed myself wrongly, they are retained, however you cannot select the entire spreadsheet and double-click the column width or row height, it will change all to the minimum width/height.
@schiavinatto i thought that you meant something else but I wanted to clarify for elyseg that column widths are saved. Except in csv of course.