PAL the format has a higher resolution but DS9’s production process was for NTSC. They would not have redone the series in PAL so that version is likely scaled the lower resolution up to the PAL resolution along with the speed artifacts described.
I think the AI upscales we have now are a novelty but not a substitute for the DVD masters. Additionally, Marvin Rush used specific camera techniques to isolate characters from the background in the early seasons which in hindsight can the image looks undersaturated and muddy.
LCD technology is pretty poor at scaling up non-native resolutions, even in 2026. DVD is probably the best quality but your mileage may vary based on the screen you use. Streaming imposed an additional penalty due to additional artifacting from the low resolution and the usual penalty of increased blur and smudging during camera motion.
Counterintuitively, using an old CRT screen or a filter component like ShaderGlass or RetroArch will process the image in such a way that tightens up the blurriness the image and will let your eyes relax.
As much as I wish DS9 HD was a thing, it will almost certainly remain an artifact of contemporary production. There are ways to mitigate that reality, but no way to change it.
RetroArch should have a video player built in. Anything running in RetroArch should be able to run its shaders.