optical flow and frame blending haven't worked on speed ramps for about 7 years

I'm joining this thread, as I'm having the same issue -- can adjust speed, but only in Frame Sampling.  Frame Blend and Optical Flow are "options" but neither actually do what they purport.  Specifically, Optical Flow is what I need.  Sounds like the old solution was to enable Software Rendering in Project Settings, but Adobe eliminated that in v2025.  So how do we get this to work now?

Mac OS 15.7.1
MBP 13-in M1 (2020)
PPro 25.4.1

I've been doing more speed ramps and I realised this as well. Its ridiculous how the supposed industry standard editor can't even get basic features right. Would be nice to be able to speed ramp then slow down to under 100 without having it look like a stop motion video. 

Seems like the only "workaround is to manually cut out the constant speed parts and remove the speed keyframes, which messes up the clip so you then have to manually match it to the start of the ramps. Either that, or be forced to stick to 100% speed.

I dont think it does work.  Its not worked through 2 or 3 pc's and numerous Ppro versions, its very unlikely that I've had a special config that has made it not work for years.  You can tell when it works when you render a time remmaped optical flow sequence and its takes a while to complete, if it does it in the same time as usual, it looks like its working, but its not.  

The staffer was asking for additional information, it seems, because on their system it works. So it would be a valid question.

whats the point? if nothing has happened in the last 7 years (and I saw it bug reported when it first broke), aren't we just wasting each other time?

its not worked in the last maybe 5 or 6 versions of premiere, so take your pick