Just to chime in on this. AES publishes a pretty good read on the subject: https://www.aes.org/technical/documents/AESTD1004_1_15_10.pdf
They are to my knowledge the best standardization of LUFS, but yes the different streaming services could have their own standards. One thing to note is that on Spotify you can actually turn this feature off in the settings.
I personally settled at -14LUFS being the loudest I’m willing to go anyways. I have pretty decent HiFi listening gear and love the way music with a lot of dynamic range sounds(classical). So for most material I work on I try to capture that same listening experience. It’s actually hard to get to -14LUFS most of the time.
● It is recommended that the Target Loudness of the stream not exceed -16 LUFS: to avoid excessive peak limiting, and allow a
higher dynamic range in a program stream.1
● It is recommended that the Target Loudness of a stream not be lower than -20 LUFS: to improve the audibility of streams on
mobile devices.
● It is recommended that short-form programming (60 seconds or less) be adjusted by constraining the Maximum Short-term
Loudness to be no more than 5 LU higher than the Target Loudness: This ensures that commercials and similar short-form
content are consistent with the stream loudness.
● It is recommended that the maximum peak level not exceed −1.0 dB TP: to prevent clipping when using lossy encoders.