Which are your settings in Settings > General > Reading & Display?

Select the message and hit R.

Selected "View attachments inline". Nowhere is a selection to automatically MARK AS READ.... (which it used to do and unbold it...automatically.

Clicking R does indeed unbold. But it should do it automatically. Can't find the selection to automatically MARK AS READ.... (which it used to do and unbold it...automatically.

Selected "View attachments inline". Nowhere is a selection to automatically MARK AS READ.... (which it used to do and unbold it...automatically.

I showed you in the image in my first answer!

Clicking R does indeed unbold. But it should do it automatically. Can't find the selection to automatically MARK AS READ.... (which it used to do and unbold it...automatically.

Please have a further look on my first screen shot and the second one I'll post in this reply! To open a new tab with "Settings" click on the ≡ "Hamburger" button in the upper right corner of the TB main window and select "Settings". In the Settings tab select "General" and scroll down to "Reading & Display" ....