Volume sliders never sound linear to me

Ironically that is because (with very few exceptions) every application from OS-s to streaming service webapps to games to mediaplayers uses linear volume slider. Human hearing is logarithmic.

The way typical volume slider works is multiplying the audio sample values with a coefficient that is ≤1. Ie, if you set volume to 50% the input is multiplied by 0.5 and as a result the signal voltage level on the analog output to your headphone or loudspeaker drivers is halved. The kicker—halving the voltage is just 6 dB less volume. This is why if you have sensitive headphones (or big, powerful speakers) you find that you have to keep the volume slider in your OS at 10% or even lower to not blast your ears off. And why the upper half of volume sliders is completely useless.

I have an unconventional speaker setup that makes classical analog volume control completely impractical. Since said setup has the maximum sound pressure level output of around 110 dB at full scale digital input, I have to keep the OS volume slider at 30% and in-app volume sliders at around 20%, resulting the total multiplier of 0.06 (or about -26dB full scale) to have comfortable volume levels. Only exception is Elite: Dangerous; with sound set to full dynamic range I can keep the main volume slider at maximum and enjoy glorious dynamics. Youtube is also surprisingly reasonable, probably because they normalize to -14dB LUTS or something similar.