This app was mentioned in 9 comments, with an average of 1.33 upvotes
I've had good luck with https://play.google.com/store/apps/details?id=com.samay.markasread2, it works pretty well for me.
https://play.google.com/store/apps/details?id=com.samay.markasread2
Does nothing but add the mark as read option to Gmail notifications.
https://play.google.com/store/apps/details?id=com.samay.markasread2&hl=en This is what I use, it works mostly fine, there are a few bugs.
I use an app called "MarkAsRead for Gmail".
https://play.google.com/store/apps/details?id=com.samay.markasread2
Mark As Read adds a 'Mark As Read' button to a Gmail notification. https://play.google.com/store/apps/details?id=com.samay.markasread2
Now if someone knows a way to remove the 'archive' button..
This app does it without tasker.
https://play.google.com/store/apps/details?id=com.samay.markasread2
Edit: jeez just trying to help people out who don't want to go the tasker route lol..
Install MarkAsRead for Gmail (beta). It adds the button to the notification.
https://play.google.com/store/apps/details?id=com.samay.markasread2&hl=en