As usual the guys have provided some excellent suggestions for sharing the iTunes/Music library on multiple Macs by keeping the library on an external drive. I used to do this and IIRC all of the metadata, playlist counts, etc. are preserved as long as you're talking about the same user account each machine.I don't do that anymore because I decided to pop for an Apple Music subscription which does the same thing and I can access my music on almost any device that I can use to log into my account.
If you have your library on an external drive iTunes/Music does the following:
1. Once you go into preferences/settings and tell the program where the library is iTunes/Music looks in that location every time it launches. If you want to temporarily change the location/use a different library hold down the Option key during launch.
2. If you don't have the external drive attached when you launch iTunes/Music it looks in the default location on your boot drive. If you ever forget to attach the external drive before launching iTunes/Music, the easiest thing to do is to close the app for a moment, attach the drive, then relaunch the app.
If you want to have several different libraries then you can do as you said and ho9ld down the Option key while launching the app to choose the library you want to use. I used to forget to do this I think I created a launcher script that did this for me.
As someone who also has vision issues I agree with you that both of these programs could be improved significantly in that regard. Apple has made many accessibility improvements over the years but these programs seem to lag behind.
Here's a page that outlines the current state of this issue on Apple products. Near the bottom of the page is a link where IIRC you can send relevant comments to Apple.
Find information about Apple's built-in accessibility tools and technologies that help people with disabilities get the most from their Apple products.
support.apple.com