I tried manually copying the DLL30 to VLC 4.0 and VaporSynth doesn't show up in the Filters tab.
I also faced an issue where SVP Manager fails to copy the file saying it doesn't have write access but I did grant "Users" full access to the VLC folder.
Then I tried manually copying the DLL30 to VLC 3.0 Portable folder. It worked, VaporSynth did show up as it should, but when I activate DEINTERLACE there's no change in image smoothness, it feels like the FPS is the same. And that green message at the bottom "Playing at 59.xx FPS" doesn't show up, but when I deactivate DEINTERLACE the green message comes up saying "Playing at 23.xx FPS". So basically it's not working for me because in the very end the FPS smoothness isn't achieved.
This is the exception that shows up in the Event Log:
09:20:09.382 [i]: Profile: using auto values [4]
09:20:09.406 [i]: Playback [28d0]: playing at 59.9401 [23.976 *5/2]
09:20:09.532 [E]: VLC: Python exception: SVSmoothFps: unable to init GPU-based renderer - code 131072\n\nTraceback (most recent call last):\n File \src\cython\vapoursynth.pyx\, line 1927, in vapoursynth.vpy_evaluateScript\n File \src\cython\vapoursynth.pyx\, line 1928, in vapoursynth.vpy_evaluateScript\n File \C:\Users\fernandi\AppData\Roaming\SVP4\scripts\28d0.py\, line 51, in <module>\n smooth = interpolate(clip)\n File \C:\Users\fernandi\AppData\Roaming\SVP4\scripts\28d0.py\, line 34, in interpolate\n smooth = core.svp2.SmoothFps(input_m,super[\clip\],super[\data\],vectors[\clip\],vectors[\data\],smoothfps_params,src=input_um,fps=src_fps)\n File \src\cython\vapoursynth.pyx\, line 1833, in vapoursynth.Function.__call__\nvapoursynth.Error: SVSmoothFps: unable to init GPU-based renderer - code 131072\n
09:20:09.532 [E]: VLC: script evaluation failed
09:20:23.184 [i]: Profile: using auto values [4]
09:20:23.217 [i]: Playback [28d0]: playing at 23.976 [23.976 *1/1]
09:20:38.816 [i]: Playback [0]: disabled while video is playing
09:20:38.829 [i]: Playback [0]: deleted
09:20:38.830 [i]: VideoPlayer: VLC disconnected