I have installed Notes 8.5 for Linux on two different systems that both show this problem:
The Insert key does not always work, to toggle read/unread.
This has never happened to me before, so I assume it is 8.5-specific. The problem is only with some messages - it seems like simple text messages and Notes email works normally, while HTML messages (internet email) is not possible to mark read with the Insert key.
Subject: thanks for pointing it out
it has already been captured in bug report.
On Windows,
If you don’t have preview pane open, Insert key works.
If you have preview pane open, focus goes to the preview pane and Insert key won’t work.
You can also click on the message to give table focus before hitting Insert.
On Linux, giving table focus then Insert doesn’t work.
If you don’t have preview pane open, Insert works (on Linux and Windows).
Subject: Your details apply to my situation as you describe
thanks for the feedback