Itunes wont let me add mp3 music files to the library. I have made sure all permissions are ok but to no avail. I am on a PC with the windows 11.

YouTube allows you to watch content on their site. In the case of copyrighted works it is up to YouTube to provide appropriate compensation to the rights holders. YouTube does not grant you the ability to download the audio content of a YouTube video so that you can use the audio where and when you please at a later date. Using a third party utility to circumvent that limitation doesn't legitimise your actions.

See https://www.youtube.com/static?gl=GB&template=terms, in particular:

The following restrictions apply to your use of the Service. You are not allowed to:

1. access, reproduce, download, distribute, transmit, broadcast, display, sell, license, alter, modify or otherwise use any part of the Service or any Content except: (a) as specifically permitted by the Service; (b) with prior written permission from YouTube and, if applicable, the respective rights holders; or (c) as permitted by applicable law;

In addition I refer you to section B.8.ii of the Apple Support Communities Use Agreement - Apple Community:

Do not submit software or descriptions of processes that break or otherwise ‘work around’ digital rights management software or hardware. This includes conversations about ‘ripping’ DVDs or working around digital rights management software used on Apple Music or other media sources.

tt2

Don't listen to these people, this problem has NOTHING to do with files ripped from YouTube. (There is no way they'd know the source of a particular file.) I've been having the exact same issue with music I ripped from my own CDs or files that I bought from other sources. This is an Apple problem. It's been going on for at least two weeks now and it's wreaking havoc with my library. There is some kind of sync issue going on behind the scenes. I use both a Windows computer and a Mac, and I'm seeing two different libraries - one in iTunes on Windows and another in Apple Music on my work Macbook. They get out of sync with one showing files that are not available on the other. It's a mess.

What is the source of these mp3 files? There have been a number of reports lately with imports failing for content ripped from YouTube videos. Don't do it, it is a breach of the terms of use. Buy songs from official outlets like iTunes, Amazon, Bandcamp, etc. or watch them on YouTube along with the occasional advert.

tt2

There has been an issue of late with iCloud Music Library on Monterey not uploading changes to the the cloud. This should be resolved in macOS 12.4 released on Monday.

iTunes/Music don’t care about the source of your files, but recent changes at YouTube means that some existing ripping software is now producing incompatible files.

tt2