I’ve always used the default UI, and have appreciated it ever since they did the UI update.
For nameplates I use plater with Qazii’s profile, as does most of my guild. It’s been a game changer it regard to keys and interrupts. Willing to try out the default nameplate changes coming in Midnight just so I don’t need to cut another addon down. Will be doing the same with details when we get built in meters.
Edit: OH! I use oPie as well. Not sure if you’d count it as a ui addon, but it’s pop up menus that you can design for different things. I have one for hearthstones, one for mage teleports/portals, one for all the M+ season ports (although Blizz has now given us a seasonal pop up menu for those) and then one for character specific mounts. It’s great!