I am looking for constructive opinions about my singing. Is it almost in pitch but transposed? And why does everyone tell me that when I sing it's not beautiful?
Forget about being in tune or not. Your voice does not sound supported by your diaphragm so the quality of sound is very poor. It sounds weak and inconsistent. Some of this could be a bad recording since your voice sounds like it's going in and out. If you are not currently taking lessons then that is the bast way to improve your singing, take lessons and learn how to use your core to support your voice. It also sound compressed like you are not resonating in your sinuses. Again, lessons would help. People don't know what they are hearing they only know if they like it or if it sounds musical. Your voice does not sound musical. It sounds like you are talking in a sing-song like manner and that is not really singing.
The pitch is very inaccurate here. Even without knowing the song I can tell it's out of tune because the intervals you're singing are all over the place. But I listened to the song to give you precise advice.
Let's take your key. You sang (approximately):
fais -> com -> me-l' -> oiseau
A -> A -> B -> D#
It should be, in your key:
A -> A -> C# -> E (assuming the first and second notes are meant to be the same)
Now, the A you started on wasn't an accurate A; you were about half way between A and A#. But you didn't have an accompaniment so that doesn't matter too much.
From "fais" to "com", you sang A to A. I don't know if that were intentional, but the original song goes up 5 semitones between 'fais' and 'com'. In other words, if I assume your "com" is the right note, A, then the notes are E -> A -> C# -> E. The "fais" is very short, so maybe you did that stylistically, I don't know.
The gap from "com" to "me-l'" you sang an interval less than 2 semitones (sharp A to slightly less sharp B). The original has a 4 semi tone gap.
From "me-l'" to "oiseau" you sang slightly less than 4 semitones (sharp B to D#), but the "oiseau" you sang went higher and higher up another semitone to E. The original has 3 semitones here.
Because of how inaccurate it is, and also how your tone is not great, a teacher is the way to go. Self teaching will be very hard. BUT, I understand not everyone can afford that so if you really want to work at home... learn to sing a major chord. So that's C E G. Or in this key it's A C# E. "fais comme l'oiseau" just opens on a major chord. If you can sing a major chord, you can sing the first words of this song. Download a piano app, play C, E, G and sing the notes, up and down.
And why does everyone tell me that when I sing it's not beautiful?
Because it's not in tune. Pure and simple. If the first note is in tune then every other note is out of tune with that first note and with all the other notes.
If you can't hear this yourself then it may be that you are tone deaf. There is an online test for this here. Whether or not it is any good is difficult for me to say. I tried it and scored 100% (i.e. not tone deaf) but it is inconceivable to me that anybody could do the test and not score 100% in the same way that I can't conceive how somebody who is red-green color blind can't tell the difference between red and green, this despite the fact that one of my brothers is red-green color blind.