It's funny how the things people love the most and grew up with don't seem dated to them.
They are very dated. From the bus seat costumes to the flat, un-animated touchscreens with less functionality than the phone I'm typing this on to the sexist outfits and sometimes awful makeup on the women to the messages of episodes like "The Outcast" which do not go over well in the 21st century.
I’m actually a new Trek fan. I only just finished watching DS9 last week. TNG I finished in 2015(it took me so long to dig into DS9 because I desperately wanted an HD remaster but when I kept reading about how that was not going to happen anytime soon, I took the plunge thanks to the pandemic. DS9 is by far my favourite Trek show. It blew me away). I don’t think DS9 feels dated from a design stand point. Some of the execution of those designs can look a bit cheap but the design itself looks fine. Meaning you could make DS9 today, with a bigger budget & keep all the equipment & ship designs & props but made to a higher production quality stand point and it wouldn’t look dated one bit. What gives the show away is the 90s production technology & techniques. You can tell it was made in the 1990s because of Major Kira’s hair cut, that sort of thing.
Early TNG does feel dated. The first couple seasons. But again it mostly feels dated because of things like an actors hair style or the production technology. The movie sets of TNG don’t feel nearly as dated. Why? Larger production budget.