The definition of lossless is that either no compression algorithm was used or the compression algorithm is capable of precisely recreating the original bits in as bits out. If you feed a lossless mechanism an 8 bit 3.5KHz mono bitstream, it must reproduce the same 8 bit 3.5Khz mono bitstream at the other end. Quality out equals quality in.
In your definition, no sound is ever lossless because no microphones can ever capture the complete audio experience available from a live performance - if you move your head a quarter of a wavelength, the sound will change.
That's why we don't use that definition.
Also, I’m aware SACDs exists. I actually have an amp that can decode DSD encoded audio but I failed to hear a difference.
Yes, if you blast humans with enough energy in any form they will eventually notice. This is not a relevant result for music.
110 dBSPL represents thousands of times more energy (in watts) than you could plausibly expect in any musically derived ultrasonic content played at a volume level which doesn't pose a significant risk of permanent hearing loss. At such insane power levels, obviously nobody will be hearing the actual frequency but rather sub-harmonics and/or other physical sensations derived from that moronic level of sound pressure.
Because from all accounts it is a myth.
Sensitivity to audio falls off a cliff as you approach 20KHz.
Especially if your hearing has been damaged by repeat exposure to 19 kHz at 138dB SPL.
From all accounts? Don't you mean from one account?
CDs aren't lossless unless the material was recorded at or below 16 bit/44.1kHz.
You can argue whether the difference is perceptible - some blind studies suggest not - but this fact is what led to a variety of semi-obscure audiophile disc formats that offered higher sampling rates (https://en.wikipedia.org/wiki/Super_Audio_CD).