I did actually figure something out but I think UE5 is still limited and later updates will fix more things. The space switching was completely broken by this.
I figured out that the transform tool requires selected the keyframes in the sequencer view not the curves view. I then scale things by -1 and then translate them forward by the length of the animation. This technically does what I expected but not as correctly as I hoped which will probably be fixed in the future.
Maybe I can work with this at least. I somehow had to transform the animation by *-1 then by +30 then by *.5 to at least get it somewhat correct. I may be able to manually fix the space switching from here. Oh and I used Windows 10’s game footage recording feature so it didn’t capture the popup menu where I selected the transform tool, but everything else in this video shows me roughly getting a mirrror animation effect working. Even here though timing is way off. The last frame should be 25 not 15.