RPGMemes

This is an excellent suggestion that I completely forgot to mention, simply because I don't use it myself. (Online, I use Foundry and keep the total secret, in meatspace I use pen and paper behind a screen.)

Many tables really like this approach, because nobody needs to remember anything and everyone has the info to hand. If you have forgetful players, or players who don't pay attention 100% of the time, or if you need to put your information tracking in a public space (e.g. because you run on owlbear, or play on a small table with no DM screen) this lets you track monster HP while not writing down anything the players don't know.

DM's: Definitely consider this approach if your players are constantly asking you questions like "how much damage did this ogre take again?" or "which of those two minotaurs has taken the most damage?" - it can really help you out.