I setup the partition to FAT32, about 230 GB in size. I plugged it in and went through the Tesla menu in the car. The DashCam was no longer grayed out like I mentioned prior so I turned that on and tested, works great. However, Sentry Mode was grayed out no matter how I interacted with it.
Then I fired up the Tesla app from my iPhone and selected "Controls" menu option. On the screen you see things like Valet Mode, Sentry Mode, and Speed Limit Mode. I enabled Sentry Mode by selecting the on/off switch. Then I went back to my Tesla, opened the security menu section where Sentry Mode is no longer grayed out. In fact, I disabled it via the iPhone app and saw that in the car it had also switched off, but the kicker was, Sentry Mode was no longer grayed out, just off. So...i guess maybe a bug when you initially try to enable it for the first time? I mean, there must be individuals out there that do not use the Tesla app or do not have a smartphone, albeit that must be a small pool of individuals. They would have to go through the Tesla car menu and I guess simply be SOL.
SOLUTION: So the moral of the story, Sentry Mode does work but only on FAT32 for v2020.8.3. If you have never enabled it before and it's disabled in the Tesla car menu, open up your trusty Tesla smartphone app and enable it there. It should then be accessible via the Tesla car menu, permanently as in my case.