P6 runs on Android 13, which is actually one of the few mainstream media boxes that has such a later version of Android. And DU mentioned above, security updates end in 2026.
One of the other big media box manufacturers released their "latest box" last fall (Sep 2025), and they released it with Android 12, which google discontinued security updates on Android 12 since March 2025.
There are a few generic boxes which advertise Android 14, but but they are generic boxes which you can't compare, since most don't even get any updates after delivery.
Most people do not use these boxes for very sensitive tasks. No banking, or browsing the IRS/CRA or other sites which they would be afraid of being compromised. They are primarily for consuming media, and typically behind a router using NAT anyhow, so rarely facing the outside world. So unless you sideload some sketchy app or addon for some package, there is very little risk of anything. And if you suspect something, a simple reset, will clear it to factory settings, if you were smart enough to take a backup of your servers/favorites,etc.. you can restore your backup and be back up in less than 10 minutes.
So there is really nothing wrong for these purpose built devices to run older versions of Android (Andoid 9 and 11 are also very popular for media boxes).
And unless you have a "certified" box for netflix, disney, etc. you will always have to jump through hoops unless you sideload custom mods. And you say "plex" ? What is wrong with plex. Not a huge fan of it, but it works. I have Plex server running on one of my synology, and plex client on most of my buzz boxes and it works.
It all comes down to what you want to do with the box. But as a media player there is no super critical need to have latest security fixes. How many new Android TVs out there are still being sold with Android 13 or lower ? You'd be surprised.