It looks like there's a bug in the Edge Flange tool in 2019 SP4.  Can anybody replicate this?  I have attached a video that should make it crystal clear, but basically you can create an edge flange on a curve, but only propagate it in one direction to a tangent edge.  If you try to select the other direction it fails.

Is this only in 2019 SP4?  I have attached the sldprt, just for anyone to verify.  Is this also a problem in other versions?  It's easy enough to replicate the part to check.

Edit to add:

This looks to be regressive behavior.  If you go in one direction you can at least get the edge flange to take. (appears not possible in 2019 SP4 above). See how it works in 2019 SP3:

And finally, it works in SW2020: