True-up Removed?

Maybe. I had some questions about how to use edge explore 2 and fr965 and this is what the Garmin agent wrote. It's not strictly about TrueUp but as far as I understand it is probably related:

"The benefit of recording it on your 965 would be that the watch and Garmin Connect would line up Training Status-wise. You used to be able to toggle between different device's Training Status's, but that's no longer the case. The goal of that change was to make your Training/fitness data more seamless and unified. If you record an activity on the Edge, the Training Status that shows on the Edge won't be the same as what is displayed in Garmin Connect.

IF you had an Edge that was compatible with Extended Display, you could have started an activity on the watch and then used Extended Display to show the data fields on the Edge. This FAQ explains how it works and lists the compatible devices: What is Extended Display Mode?

Since you unfortunately don't have Extended Display, it makes things more limited. You could technically start activities on both devices and then just delete the one recorded on the Edge like you were thinking...otherwise you may get some strange information in Garmin Connect with double activities. You could also perform the activity on the Edge only and broadcast your heart rate from the watch....but then you'd be recording the activity on your non- compatible Unified Training device. "