Pretty much any decent Sound Card will outperform 99% of the onboard ones.
The best way to verify how good or bad the onboard is, is using some decent headphone. Easier to notice than using speakers, at least for the average user.
But note, by decent headphone, I mean some Studio/Monitor ones, without the clipping bass heavy profile of most shiny celebrity-associated brand.
Don't have to be an expensive one, though.
Yesterday, while I was testing the Soundblaster G6 on the telly, I tried to use the onboard from the Asus X570-F, and isn't horrible, but even without any adjusts, the Soundblaster G6 gives a much richer sound, not just louder, but much more detail (for speakers). For the headphone is like going from the TV speakers to a mid-range dedicated speaker. Yes, that much, for detail, plus much louder.