These days, what used to be referred to as "the holy grail of the misinformed" is getting closer to actuality.
There are now applications designed to do exactly this task - isolate parts of a complete mix & allow you to change their relative levels; including total removal or isolation of sections such as vocals, drums, bass or 'instruments'.
Results are not perfect every time, but are getting reasonably close these days.
The most comprehensive of these so far is iZotope RX [curently at v8, though I only have v7 to show images from] Various versions from 99 to 1000 USD.
iZotope has many audio cleanup functions, but here is the Music Rebalance plugin, which can isolate 4 types of music data - Voice, Bass, Percussion, Other.
After that, a new kid on the block [Mac only at the moment] is Neural Mix Pro, free download, but 50 USD to enable the save function.
It's less comprehensive than RX, but it is real-time & needs no pre-processing.
Results can be a bit phasey but it doesn't do too bad a job.
It opens by default showing your iTunes music library, but you can drag & drop files to it too.
It can do other tasks, somewhat DJ-oriented, such as time-stretch & pitch-shift but they're not under consideration for this QA.
As new products become available, please add to this starter list.