i always try to do the sandwich method unless it seems the creator is asking directly for mostly critique instead, but otherwise i do [compliment] [thing to work on] [compliment]
it leaves the person to see what they did right as well as what they can improve on to fix things for the future without making them feel like they did a lot wrong!! i also try to limit the thing they need to work on down to 1 thing so they don't get overwhelmed if there's a lot more (unless again the creator asks otherwise)
for example if someone's mix is muddy but the sound of the utau is really good and the tuning is pretty nice i'll say something like "hey!! i really like the utau you used on this, they have a really nice tone!! the mix is a little muddy, maybe you could bring the higher frequencies out in EQ to bring out the consonants more? but like wowowow that tuning!! oooo its so nice!!"
that way they still feel positive about what they did right and still get the message for future works on how to do better
imo it's also important to realize some people aren't looking for critique. like i don't want to pursue visual art seriously anymore, so i don't like getting critique on my sketches because it's really not my thing and honestly i don't care about the improvement, i just do it for the fun of doodles.. so it really just depends on how they present the thing!! if it's something they seem to want to improve on, like, more than just a hobby (whether that's to get "popular," get money out of it, etc.) then i think critique should be expected, but if they say something like it's something they just want to do stress-free on the side, you should ask first before giving critique with the same sandwich method like (compliment) "do you want critique? but also" (compliment)
as for going too far? i think that depends on the person as well. if the creator directly expresses that they want all critique on what they need to improve, i think the sandwich method can be lifted to put in as much information, with how to fix the things you're saying, as possible. if they don't express that they want much critique, too much can discourage them!! so you need to limit how much you give at once. if you're giving the only the bad of their work without a way to improve it, that's not really too far, that's just not constructive and you need to give them a proper means of improving what they had wrong.