On Mac the Options dialogue box is accessed according to Mac usage. I think you might still be able to disable OpenGL.
[EDIT]
The first part of this comment might be irrelevant. Once there is a number in the line width field it seems to stay there. So long as you are aware of the issue you should be able to work with it.
yes you can, though for some reason they call it OpenCL not GL (sorry about the delay replying - apparently I used up my quota!!!)
No good I’m afraid - my Bugzilla login/password (as confirmed by Firefox) was met with “…not valid”. So I tried to set up the account again, and was told the username was already taken. Catch22.
OpenCL is used in Calc for larger calculations. It can be disabled if it causes issues in calculations but is not often a problem.
Click top menu bar: Format > Line…
This will bring up the line properties dialog box.
see my reply to Hrbrgr above ^ ^ ^