To be clear, The CEC software from HamsKey.com (KD8CEC) does not work with the version 6 (v6) display. The v6 driver software required takes up a significant portion of the available program memory in the Nano on the Raduino. That leaves little room for the enhanced features of the CEC software and vise versa the CEC software takes up most of the available memory beyond the base functioning of the rig control. So in my opinion, unless you want to buy a new screen, then the CEC software is not compatible with the v6.
It DOES work with the rest of the version 6 IF you change out the display to a Nextion 2.8" as Mike G4GOU stated in his message.
You should do the research on the different sites like hamskey.com, ubitx.net and general internet searches before you decide to upgrade or change the stock version 6 ubitx. For the prior version the choice to go to the CEC software was not a significant cost and could easily be reversed. The CEC software would work with the (at that time) standard 2 line display (16x2). There was also not a graphics option like either the version 6 screen or the Nextion screen that CEC provided. Of course there was extra cost to purchase the Nextion screen then as well, however the cost of the kit was less by about the amount of the Nextion screen (ignoring the case which had to be purchased from 3rd parties).
Above are my attempts to clarify your choices and provide some of my interpretations of options. Please be sure to do the research, as there are many who will have different opinions that may closer match what it is that you want.