Really confused about loudness

(Yes this is a long post but I don't really know how to explain my questions in a few sentences.) For the past year I've been learning a lot about mixing and mastering music. Loudness is of course very important in these. Even though I've learned a lot already, there are still some things that don't make sense to me and are really confusing.

I've learned that when it comes to loudness the 2 most important things are integrated LUFS and dB true peak. For a short time I have been mastering my music to about -14 LUFS integrated which is what Spotify recommends. I quickly learned that that was unnecessary and that the integrated LUFS should be as loud as long as the song still sounds good. But then there is still the dB true peak. Spotify and other streaming services recommend -1 dB true peak so when the lossless audio file gets converted to a lossy format, there will be some headroom to prevent unwanted converting distortion. I have stuck to this rule for quite a while now. However I learned that a lot of popular and more professional artists have songs with audio above 0 dBFS. So is there even any converting distortion? Or is it just so small it's barely noticable?

When I'm watching a video to learn more about the song creation process, the person in the video sometimes uses a reference track. The reference track almost always has audio above 0 dBFS. If I understand correctly, audio files with a bit depth of 32 can hold audio above 0 dBFS, but 16 and 24 bit depth audio can't. And when a 32 bit depth audio file with audio above 0 dBFS is played, it will always get clipped to 0 dBFS by the audio system. I hope I've learned this correctly. For quite some time I was confused because if you want to match your song to a reference track but that reference track has peaks above 0 dBFS, how does the integrated LUFS even matter at that point. You could just make both the integrated loudness and peak loudness louder and louder. But if audio is always clipped to 0 dBFS then that would solve that question. Where you would get such a lossless audio file of a song is another thing. I guess you have special websites for that where the artist uploads the lossless file which people can then buy since most if not all streaming services are lossy.

A few days ago I wanted to experiment some things myself. I got a really loud (about -0.5 LUFS integrated) dubstep demo track from a sample pack. It has a bit depth of 16 meaning it has no audio above 0 dBFS (at least I think.) I connected it to the master bus that only has a Youlean Loudness Meter, no effects. When I play the track the default meter on the master bus shows that the maximum loudness of the song is 0 dBFS. Somehow when I look at the Youlean Loudness Meter it shows that the true peaks are hitting about 3 dB. The meter on the master bus can show audio above 0 dBFS so how are they different? Then I also put an ozone 10 on the master bus just to check the meter and it shows about the same as the Youlean Loudness Meter. The weird thing is is that I thought audio files with a bit depth of 16 weren't able to hold audio above 0 dBFS. How is all this possible?

People always say "don't look at the numbers. If it sounds good then it is good." But what if I made a song that had audio above 0 dBFS and I thought it sounded good. I then go to export it and it still sounds good. Then I upload it to streaming services and on release I listen to the song to hear if it still sounds good, and it sounds terrible. Updating a song is not common and I think it is quite a hassle to do. So I don't want to risk uploading a song and having it completely ruined this way.

I hope I explained all this correctly. I just want to be done with all of these technical problems and just be creative and have fun making music. If anyone has answers to these questions I will be very thankful.