I am using Quip commenting extra in Modx. There are some distracting bugs but the biggest issue is that Quip is not Modx3 compatible and it is not being updated anymore.
Does anyone have recommendations for other more modern commenting extras in Modx?
You can try https://en.modstore.pro/packages/users/tickets or https://en.modstore.pro/packages/utilities/easycomm As far as I know both of them will be compatible with MODX3(probably already work, I know that the authors have already dealt with compatibility)
Alternately you can always use MODX-independendent disqus.com :)