There doesn’t appear to be an obvious way to mark what has and has not been read. I do see a line for last visit, but that doesn’t mean that I have read everything below that line. E.g., I tend to let METAR go and read it in large blocks, but visit other boards multiple times per day.
I also don’t see a tag for the prior board called RB: Investing Strategies.
I am also seeing posts with tags I was not subscribed to like my-dumbest-investment and your-investor-journey and just-ask.