2000s digital anime looks different from 2020s digital anime for the same reason that a comic produced in 1935 looks different from a comic produced in 1970.

Artstyles and preferences change over the decades even if the technique or tools don't change too much.

2000s anime is almost entirely digital.
There's some anime from the late 90s and early 2000s that were a mix of cel and digital but such a thing was still rare and most "cel and digital" hybrid anime was moreso a hard-shift mid-production to digital, not using cel and digital together. You see this in shows like Mahoromatic (first season is cel, second season is digital), Galaxy Angel (first season is cel, second season is digital), or Inuyasha (first 100ish episodes are cel, the rest is digital).

The anime in your gif was entirely digital.