I noticed jagged text on a computer running Windows 10.
It was particularly noticeable with Firefox and Chrome.
I opened Advanced display settings and tried to open ClearType text.
However this failed with this error message:
C:\Windows\system32\cttune.exe Windows cannot access the specified device, path, or file. You may not have the appropriate permissions to access the item.
Instead I tried to start cttune.exe directly:
This was possible and I noticed that ClearType was disabled (as expected).
I selected: Turn on ClearType
And completed the guide to adjust ClearType optimally.
That solved the problem. After enabling and adjusting ClearType, text in all programs looked much better without jagged edges.