Wow! This has been an experience.
To answer an earlier question, my MacBook Pro is Mid-2015.
I still have not been able to upgrade on my own, but I was able to get into a Best Buy and talk with Geek Squad, since I have the full service contract. For some reason, when I purchased my MacBook Pro, I was told to install Parallels Desktop for a couple of programs I was using at the time, but I ended up purchasing another notebook computer, an HP with MS Windows and never used the Parallels Desktop. Maybe (the Geek wasn't for sure, but said there is no hardware reason my notebook was not App Store upgraded to Mojave or Catalina) but maybe because the MacBook hard drive is split for the Parallels could have, don't know, but could be a factor. Again, I am not a computer whiz only a user.
Long story short, I was told because of my service support with Geek Squad, I will only need to purchase a backup hard drive and then Geek Squad will completely back up hard drive, clean hard drive and install the latest Apple OS. I'll be without my computer for 2-3 days. I was told the Geek would upgrade from El Capitan to Sierra, High Sierra, Mojave and finally latest version Catalina.
I'm busy and cannot give my MacBook until after first of December, but If this is the course of action I must take, then after I get my computer back from Geek with JDM re-installed, I'll provide an update post of results. All this for which started out just trying to update my 30 day IFR cycle for my 2 Garmin 430's, as I have done for the past 10 years.
Just like building, it takes measuring, cutting, filing, sanding, fitting, trial fitting and final fit.
Thank all of you whom read and contributed to this cause. Sometime's it takes a village.
Sincerely,
Kenny Gene
Wichita Kansas area Aviator
Rv7a AWC 9-07 690 hrs sold 11-11
Rv10 AWC 10-10 849 hours