As far as I know YouTube is currently very picky to monetize videos like the ones you posted (just a picture and music) since these videos were often automatically created in the past to abuse the monetization system with high watch times. But no one is actually watching them because they are just played in the background and therefore nobody sees the ads on these videos.
Advertisers are not paying for this and because of that these kind of videos often fall under "reused content" and cannot be monetized.
Just do what you love to do and is fun. I just wanted to tell you that you shouldn't expect to be able to monetize such videos. If it works consider yourself lucky.
I think the best idea if you want monetization is to create an original video for each of your songs but this could be very hard if your music is hours long. Maybe take a long walk in nature and record that to video.
@TENG Yes, that's totally possible. With Music Maker you can create your songs out of short audio loops (sold separately, you would need a commercial license in your case) which is very easy and fast to do.
Or you could record with virtual audio instruments (sold separately or many free ones which are available on the internet). But for creating songs with virtual instruments I would suggest you try Samplitude Music Studio because Music Maker has some severe bugs.
Thanks @SP.! I am not a musician and don't know any instruments. But i would like to make songs by mixing and combining songs or beats to make a new song. Then put it out as mine.
Whats the best possible ways and software to do it?
If you use just short loops and combine them to create a song then your finished song is yours. You will never own the rights to the loops but you own the rights of the song you created with them. And you can monetize your song. But other people can use the same loops as you and can make songs that sound very similar.
If you use parts of other songs you need to release them with a label that pays royalities to the original composers and artists that made the original song or else it would be copyright infringement.
With these five soundpools you can experiment and see if you like to work with Music Maker. This will cost you nothing at all. But you cannot release the songs you create for commercial purposes.