Probably location dependant.
No change for me, I live and work in the west, daily commute using public bus service, no peak time MRT ride in general.
Quick test opposite Jurong Point.
Check out my Speedtest result! How fast is your internet?
https://www.speedtest.net/my-result/a/11906049038
There are of course slow places like in some lifts or NSL underground MRT Stations, but not getting worse recently.
if compared to the 5G SA+NSA time (before 30 June 2026), then yes there is a bit of depredation, for example in some lifts or other low signal areas, from 5G NSA to 4G.