Starting a YouTube Music Channel

I want to start an YouTube Music Channel like Central Bass Boost, Trap Nation, Majestic Casual they have 100+ music videos that include popular artists and I am wondering how they can use them without copyright issues?

I tried to download songs from soundcloud licensed under a Creative Commons License and upload them to my YouTube channel and they still got copyright flagged

You can create a channel using copyrigted music (if they give you rights to do so or you can do it without rights and hope to not be striked) , but you will not be able to monetize your channel due to re-use content policy in the YouTube partner program.

your best bet would be reaching out to lesser-known artists (that still get good amounts of views) and then eventually join submithub and similar services and have people submit their music to be placed on your channel.