Be careful aiming for sound isolation, it can be counterproductive.
Generally speaking "sound isolation" means reducing where sound can escape from the case, and putting some noise absorbing foam where you can to dampen the noise.
The counterproductive part is that having a lot of airflow would be the opposite of "sound isolating" -- anywhere air flows freely sound does as well. So by definition a sound isolating case has poor airflow. Poor airflow could require you to run your fans at higher RPMs to compensate, which is then introducing more noise than you would have had with a more open case that could run low RPM fans.
No idea - I remember spending a lot of time browsing Silent PC Review on previous builds to make sure I got an appropriately quiet power supply and everything else, but it stopped doing any meaningful testing years ago, and the current incarnation basically looks like affiliate link blogspam.
Generally speaking "sound isolation" means reducing where sound can escape from the case, and putting some noise absorbing foam where you can to dampen the noise.
The counterproductive part is that having a lot of airflow would be the opposite of "sound isolating" -- anywhere air flows freely sound does as well. So by definition a sound isolating case has poor airflow. Poor airflow could require you to run your fans at higher RPMs to compensate, which is then introducing more noise than you would have had with a more open case that could run low RPM fans.
Gamers Nexus did a good piece on this https://www.gamersnexus.net/guides/3391-airflow-vs-silent-ca...
(as he points out, there are still reasons to prefer sound isolating cases, it's just not as much of a clear win as it might sound at first)