I generally don’t buy into the concept of an anime with universal appeal since everyone has their own tastes. I much prefer to think that in the vast variety of anime series there’s something for everyone instead of a few series that appeal to everyone. It’s much easier to recommend series on an individual basis . As far as exploring, I would recommend subscribing to a streaming service with a variety of titles and check out series where the concept interests you even if it’s not a genre you usually watch. I doubt Romance, Sports or Reverse Harems will ever be favorites of mine, but I have come across examples that were surprisingly enjoyable.
That being said, there are some favorites of mine that tend to be pretty widely appreciated (regardless, I would recommend watching before buying if possible)
Cowboy Bebop
Fullmetal Alchemist (both versions are sufficiently different that they are worth checking out, though my own preference is Brotherhood)
Trigun
Cardcaptor Sakura
Mushishi
Death Note
My Hero Academia
Most of these are pretty mainstream, but when recommending more obscure stuff, I prefer to know a bit mire about what they’re looking for