Options - interface - friendly players Tick that box. This at least shows me friendly players’ names AND guilds. I can however find no way to NOT show guild names over peoples’ heads.
But you’re rigth the mouseover nameplate does not show Guild any longer.
It’s probably one of the many bugs. The mini-character showing broken armour or weapon has also diappeared.
We need a host of fixes to the new interface 
Now youre flagged for trolling.
Be sure to report yours (and OP yours as well) for visability!
Flagged for trolling. Gl with Blizz.
Are you Talking about the Display “Names” over all characters by default.
Or
The “Nameplates” The one’s that have a Health Bar and only come up if you hit V or Shift V (Default Keybinds)
If so. I don’t believe there has ever been a way in default UI to have someone’s Guildname in the “Nameplate”. Platers and other Addons I’m sure have it. Just not Default.
Default only shows Guild under your “Name”. But Nameplate is a completely different set of options and doesn’t include anything other than Name and Health by Default.
I don’t know if this helps you solve your issue I just want to clarify the question.
When you hover on a toon, it displays their name, level, race, class, and guild in the bottom right of screen.
When I do it , i see everything but their guild name. Everyone else has no prob seeing the guild name. I cannot. It’s a bug. Some people have it and some don’t. I had to download an addon to see what others see normally.
I don’t think everyone is speaking of the same thing.
When you used the term Nameplate it usually refers to what is directly over your character.
The Bottom Right of the Screen holds the “Tooltip”.
Sadly, Back in Vanilla we did not have that QoL improvement which is why you don’t see it in Classic, but you see it in Retail.
See this Forum Thread complaining about it in 2019.
Edit* I Hopped on a Retail Toon and a Classic Toon and with Retail Yes, Classic No, Classic Wrath Yes.
Edit 2* It seems that this is a very Loaded answer LOL. Depending on which version of the game people are running they will have very different answers.
This is the hardcore classic forums tho right? I did post this in the right place. So if retail players or Wotlk are seeing this and replying then wtf.
You 100% posted in the right place.
Which is why I loaded up the game to check and googled myself. I personally have never noticed, but your persistence seemed to indicate I might have missed something so I looked closer.
I won’t speak for the other’s.
I didn’t do anything negative to you. Keep flagging me. Nothing will happen. You got mad I tried to help you. I did nothing wrong.
If you really cared youd just block me and be done with it. You are the one here to troll.
I think that in Classic it never displayed in the “tooltip” box on hover - at least I cannot find any example of this in my screenshots. Originally it seems to have come with TBC - I even went back to my old screenshots and looked 
Hovever with the old Options UI we could choose to show or disable the Guild names over peoples’ heads.
Look at this screenshot https://imgur.com/a/J1pLOkc taken August 22, 2023.
I live EU side, so when I heard of the DF options UI coming, I logged on Era and screenshotted spellbook, talents book and all the UI options pages to compare with later - Yes, I’m a nerd
Here is your solution: /console UnitNamePlayerGuild 1
I was having the same issue. Don’t need an addon, just run this console script. Works instantly.
I’m sorry you had to deal with so many unhelpful replies, reading through them all was painful lol.
Thank you holy crap I was literally coming on here to ask this question lol
Google sent me here and this was the answer to my bug in game.
Bit of a necro thread, but go to interface, uncheck the box for Friendly Units under nameplates, its opposite of what you probably think it should be.