mvsep is the best imo ) just built the app with Nativefier )

 

UVR5 is the answer, and details have been already said in this thread before
also don't hesitate to experiment with models that split track into stems, not just vocals+instrumental, you can stitch them back easily, but results may be better

 

If you feel like paying/using credits for anything over 16bit wav output, it's possible. Using Nativefier has no impact on the output. For free? No 24bit wav output, which running UVR5 locally does. MVsep is way faster for me, but the 16bit wav output vs UVR5 24bit wav output makes the slower separation worthwhile. UVR5 allows you to set values for segment/chunk size, overlap, number of shifts, etc. This makes things a lot slower for me, but I just do it on a different Mac and don't really care how long it runs.

 

Your client has shit taste, just saying.

 

This happens because of the way this music is generated. Since you're compiling a bunch of code into the task of performing a human feeling, the best it can do is to copy and paste real performances of real musicians in a unnatural way to mimic those feelings. The results are strange instrument portamento, legatos and quantizations. Guitars that blend into polyphonic synths. All sort of weird stuff. When you split, all that flawed things start getting more attention, so it's not that RX can't split it, but the amount of crap under the hood without all the masking is tremendous.