Diablo 4's legendary items shouldn't look like the ones found by Reddit user Fr0zenberg. They aren't supposed to be yellow like rare items and some of the stats on them shouldn't exist after Blizzard's massive loot rework. Either Fr0zenberg just found the rarest items in the game or the world's first bootleg legendaries.
"I got a 'legendary' Rare item…" Fr0zenberg wrote in a post on Reddit with a screenshot of a chestpiece that should be impossible to get. The tooltip says it's a rare item but it has a unique effect that would normally only appear on a legendary. It also has a "damage reduction" stat on it, which is impossible to get on regular items anymore. One commenter thought it was so unbelievable that they accused Fr0zenberg of Photoshopping their screenshot. But when Fr0zenberg posted video proof, they took it back: "I stand corrected."
Fr0zenberg's video includes the chestpiece along with a pair of boots that have the same issue. They say they got them as quest rewards (they don't remember which ones) and that their legendary powers work despite their classification as rare-quality items. While it's probably a weird visual bug from being a quest reward instead of a drop, I didn't think it was possible for item tooltips to lie to you.
Unfortunately, both items aren't very useful for anyone with a max level character. They're both a tier lower than what you get in Diablo 4's final world tier difficulty, so they'd only help you while you're still leveling up. Damage reduction is one of the most valuable defensive stats in the game, but it's not quite powerful enough to equip low-level gear on a high-level character for. Fr0zenberg's budget legendaries are simply a novelty that will probably be bug-fixed when season 5 starts next week.
I got a "Legendary" Rare item... from r/diablo4Or you could go full tinfoil hat and theorize that these items are an example of a new crafting feature coming in the Vessel of Hatred expansion in October. Blizzard says it has plans to make rare items more valuable to endgame players who typically ignore them once they're fully kitted out with legendaries. Maybe the rumors of a level squish will come alongside a rare item rework that lets them have similar unique effects. Personally, I doubt that will be the case. It's much more likely that they'll break down into a new type of crafting material rather than becoming some kind of phony legendary. I agree with some of the commenters on Fr0zenberg's post though: they should absolutely hold onto what could become two of Diablo 4's rarest items.