WoW Forever has a "Use Raid-Style Party Frames" option, and it lives in Edit Mode rather than in the Interface settings. With it on, your party shows as compact raid-style boxes instead of portraits.
How to turn it on
- Press Escape and open Edit Mode.
- Click the Party Frames box on screen to open its settings.
- Tick Use Raid-Style Party Frames.
- Save the layout.
These steps come from the modern Edit Mode that Forever's client is built on. Blizzard hasn't written them up for Forever, but the option is there: the ClassicUI Forever addon tells its users to turn it off in Edit Mode so its portrait frames show.
Why you'd want it
Raid-style frames show health bars and debuffs in a tighter block, which is easier for healers to watch than five portraits. They're also the same frames you'll see in battlegrounds and raids, so you only have to get used to one layout.
When to turn it off
Some UI addons replace the party portraits and expect the default portrait frames to be there. ClassicUI Forever is one. If a party frame addon isn't showing anything, untick the option first.
If your layout doesn't stick
Forever saves Edit Mode layouts per UI type, according to the client's patch notes. If yours resets, see settings not saving.
For more than the default frames offer, see best unit frame addons and Cell in Forever.