Apparently it is from the Dine Out pack. "Sims are also able to host two social events at Restaurant Venues: Birthday Parties and Dates. These events unlock special interactions and moodlets such as the Flirty +2 Moodlet for eating with a special someone. You can also use the new “Feed a Bite” interaction available for Sims sitting side by side on a dinner date." (copied from simsvip Dine Out guide). I haven't tested out that interaction yet since reading this thread.
I finally tested it on PC and it works as described.
Edit: see my new post down below for a detailed explanation.
@siirysiirif it doesn't work for you and it works for mzda_grl, any mods that could interfere with this? Maybe one of them is overriding the action?
Sure way to tell would be to take out your mods (move folder to desktop), delete localthumbcache.package, reload your game and try again.
If that's not the issue, it could also be a simulationlag issue. If it takes too long for your sims to get around to do the action, they might finish their meal in the meantime. Are you experiencing lag in general?
I should have mentioned that while your Sims are on a date, sitting side-by-side, with a plate of food, before they start eating, pause it and cancel the eating interaction. Now you can select the "Feed a Bite" interaction and watch it play out. I've added a video.
