We assisted in the upgrade of a unit that was running FreeNAS 11.2. We assisted in upgrading it to TrueNAS 13.3. We did this by downloading each update from the downloads archive and manually installing them. After applying the last update which took us to TrueNAS 13.3 we no longer have the Core train available. Everything is Scale, shown below.
I am already running 13.3-RELEASE. I performed the manual upgrade last month. My (and I believe the original poster’s) issue is that after upgrading, there are no longer any CORE trains available on the update screen. Only SCALE trains are showing.