For mash-ups specifically, using yt-dlp to download music and split into stems with Demucs, using the UVR frontend, before importing into a DAW is effortless. The catch is that you can't expect to get OK-ish separation on anything other than vocals and "other", which really isn't a problem for mash-ups.
There are several. I've only tried one of them (free, can't remember which) but went back to UVR5.
While it's convenient not having to split stems into separate files beforehand, by using a VST, you usually end up doing so anyway while editing and arranging.
For mash-ups specifically, using yt-dlp to download music and split into stems with Demucs, using the UVR frontend, before importing into a DAW is effortless. The catch is that you can't expect to get OK-ish separation on anything other than vocals and "other", which really isn't a problem for mash-ups.
https://github.com/Anjok07/ultimatevocalremovergui