There are two main ways you can do it. You’ve already mentioned you have your library/music files, so that’s a good start, you’re basically looking for a way to access it on other devices. The first way would be to set up an old PC/rent a cloud server, and set up the service you want to use, though for now this may be a bit too complex if all you want to do is stream your own music, and have no experience. That being said, it’s always good to have a look and see, there may be a tutorial that works for you if you want to go down this route.
You’ve mentioned Navidrome, and it’s a good shout, basically just looks at the folders of music you have, and lets you stream them to your phone/PC (and more) like Spotify or Google Music. For the simplest possible setup, I’d recommend a service like Pikapods (https://pikapods.com), which essentially selfhosts applications for you, and gives you access to the files. For Navidrome, for 50GB storage (and the recommended settings of 1 CPU core and 0.5GB RAM), it’s $3.01 a month, which, though not free, is very affordable if that’s all you want to do, plus they handle updates, etc. You shouldn’t need to set any variables, and can upload your music to their service via FTP (File Transfer Protocol, a way to copy files to another PC/server from your PC), and they have docs on how to do that on the site.
Hope this helps :P