Ultimately it's all a bunch of compromises, and if you're doing this by hand you're probably going to be postprocessing stuff manually to cut out noise, EQ the result, etc. In this case you can use even smarter software to try to subtract at the level of tones in the spectrum, instead of at the level of the raw audio. Sometimes it doesn't work well anyway, because the tracks might have been processed differently or different instruments might be out of phase (this often happens with synthesizers and other virtual instruments, where both versions aren't the same render to audio). Soloing the tracks will automatically mute all of the other tracks for the song. The 'Solo' icon will be located on the left side where the sliders for volume are located. Click the 'Solo' icon on each channel strip that contains parts you will isolate. Separate vocals and instruments, master your tracks and re-mix songs with Moises. Solo all of the drum tracks to isolate them from the rest of the instruments and vocals. There is software that can help with this by automatically stretching and shrinking tracks in time to match them (I wrote a version of this myself). The ultimate App for music creatives powered by Artificial Intelligence. This works rather well for some tracks, but the two tracks have to be perfectly aligned for that to work directly.

Others have also mentioned that if you have the instrumental track, you can subtract it from the full track to get just the vocals. It works well with clear, well defined, loud instruments in simple tracks not so much with things buried in a complicated mix (where even a human would have a hard time picking them out).

Basically, a computer 'learns' what different instruments sound like, and can then identify the different parts in the spectrum of the full song, and then cuts out those bits separately.

To add to what other folks have said, these days you can use neural networks that have been trained to do the job.

How to separate instruments in a song