I have also been having this issue for many months and have not yet found a solution.
I use Premiere Pro CC 2020 on Windows 10, and cannot hear any sound output from Premiere to my headphones. I have Voicemeter Potato installed, but even when I fully shutdown Voicemeeter, change my output devices, and restart my PC, the issue is not resolved.
I contacted Adobe support via chat a couple weeks ago and they resolved the issue for me.
It turned out that it may not have been a Voicemeeter-related issue after all. The agent basically "factory reset" my installation by deleting/moving my "Premiere Pro" folder that contained all preferences/settings/etc. This folder was located under "Documents/Adobe/Premiere Pro". You can either delete the folder or move it someplace else so it can regenerate next time Premiere opens (if you move the folder you can save any files that may be there).
This particular solution worked for me, hopefully it can be helpful to someone else here.