Instrumental Copyright?

yes, it can. The instrumental is copyrighted by the record label

Copyright is literally the right to copy. And that is always the record label's right, not ours. Uploading to youTube is a form of copying

The entire song is copyrighted - lyrics, instrumental, live performances, studio recording. An instrumental version doesn't un-copyright a song

Yes, if the composition is still copyrighted, then any performance of it would need a license (i.e., a cover). If someone else has done a performance of the instrumental and recorded it, the producers of that record typically own the copyright of that recording, assuming they got the necessary license to record it.

Of course, like any other private property right, if they don't care to enforce it, why should anyone else care? However, it is still a violation of YT terms of service to upload things that "violate the rights of others", whether or not such others actually complain...

Yeah, you still don't own the rights to it. Make your own original instrumental music, or use something public domain or royalty free.

And before you ask, saying "I'm using this as a tribute to the artist". Unless you have the artists explicit written permission, you cannot use that as a reason