# Changes in the appearance of Mathematica 12.3 when running

I recently installed the 12.3 version of Mathematica and got a bad problem. When I want to run some Mathematica files written in the 12.1 version, the appearance of the Mathematica changes badly so that it makes a lot of trouble. For example, if I run the code

then it changes to

Could you please help me with how to figure this problem out and keep the appearance as before?

• I've seen this many times before myself since I installed 12.3. I also have 12.3 and 12.2 and 12.1 on same PC. I could never figure why it happens, i.e why everything become bold and fonts change. I assumed it is due to sharing of files somewhere between different versions. I am on windows 10. I wonder if other see the same thing on the mac. Oct 27 '21 at 8:09
• Yeah this has been driving me nuts. If you copy and paste one of these corrupted cells over itself, that repairs it. Oct 27 '21 at 14:34
• @Nasser Yes, happens randomly on MacOS as well. Oct 27 '21 at 16:22

I had similar problems when I instaled 12.3: cells in my notebook would suddenly change to a poorly-readable font which looks like above. Wolfram support suggested running the following command once as a "patch" until 13 is available:

CurrentValue[\$FrontEnd, FrontEndFrontEndObjectFormat] = "Legacy"
`

This solved the problem for me.

• Does "run once" mean once in a session, or once for all the time? Oct 27 '21 at 21:23
• @Ruslan I have not tested the above, but I am sure it must mean for all time. The command above must update the settings in option inspector and they are saved on disk. Oct 27 '21 at 22:55
• Yes, execute it once to change the preference for this setting permanently. Remember to do it again if you reset the preferences.
– josh
Oct 28 '21 at 11:42