Old mp3 aren’t recognized by music

I have a couple thousand songs on my iPad from old cd’s I have burned throughout the years. It’s an old iPad. I now have a new iPhone ( to me, it’s a 10) and a new iMac. They have these songs greyed out and won’t play them or they wont load at all. I tried uploading them to the cloud and it still doesn’t see them. I also have some songs I bought on Amazon, they won’t play those either. Why? How do I fix this? I am missing music in the car and when I work on my computer?