Thank you for the replies. Joe4, it's only available in the 365Beta and even then perhaps not all get it at the same time. Unfortunately, neither workaround quite "does it" for me. Now I know the limitation I will unfreeze as necessary, particularly when using tables. I will also only enable it when I specifically want to use i, rather than it being on all the time.
In case of interest, I found out by trial and error that it is possible to get a wider colour range for the highlight (than the standard colours offered) by setting any cell to the desired colour which then that becomes available as a "recent colour" under "focus cell colour". It seems to stick after restarting Excel, and when creating a new workbook or editing an existing one.