In the digital domain the left & right are completely separate.
In analog electronics there is usually SOME stereo “crosstalk” (leakage from one channel to the other). That can happen during recording (where it will exist in the digital file) or it can happen at playback time.
Most stereo equipment has a crosstalk spec of -60dB or better so it’s rarely a problem. (Your soundcard MAY be worse than that.) With vinyl records you can only get about -20dB but that’s still low enough that you can’t hear it under normal listening conditions.
Modern professional recording is usually done in multi-track with each instrument recorded separately and in mono. Then the tracks are panned left-to-right during mixing. If the engineer pans something 100% left or 100% right, there will be no crosstalk in the digital recording. Most stereo recordings don’t have anything panned 100%, but some do.
But sometimes a multitrack recording is made with multiple microphones and the whole band playing in the same room at the same time. In that case there will be "leakage’ or “bleed” into the other mics and when the tracks are panned they won’t be perfect.