WhatsApp ... can you

[surreysnapper]

can you mark a message as not read after you've read it

Not that I'm aware of.

You can mark the whole thread of messages as unread. I just have to swipe the thread right and it gives the option to mark it as unread

I think you can mark as unread for your own purposes but I'm not sure that would change how it appears to the sender, if that's what you're asking.

You can for your own phone ie to remind you to reply but it would still have blue ticks for the sender.

You can turn off the blue tick if you don't want them to know you've read it. But it means you can't see yourself if people have read your messages

If you are adamant that you want the blue tick for other people but at the same time want to prevent other people from seeing that you've read their messages, turn off Wi-Fi/data, read their message, close the app, and then turn those back on.