Disabling iCloud Music Library vs Local Files

1) If I disable iCloud Music Library on my iPhone will it also delete my local music that I downloaded from my PC to my phone even before I started using Apple Music ?

That depends on whether you merged or replaced the libraries back then. A merged library will keep the existing tracks when activating iCloud Music Library. Replacing the library will match for Apple’s cloud versions, essentially making a transition to all-Apple-Music.

It is a bit tricky to distinguish downloaded Apple Music tracks from other sources tracks on iPhone, while iTunes on a computer has a neat column for that.

Access your music collection on all of your devices with Apple Music - Apple Support

Add and download music and video content from the Apple Music catalog - Apple Support

2) If I cancel my Apple Music subscription, knowing it will delete the music I acquired from the service, will it also delete the local music downloaded from PC to iPhone ?

Only the music from the subscription will be removed when you cancel. If you have files from other sources your library, then those will stay. However, if you replaced your library then those songs may have been swapped for cloud versions, which are part of the subscription, and may get removed.

Basically I'm just looking to save my local music ; I usually keep it in my computer but my computer screen is broken and therefore unusable for some time ~ thanks for helping !

“Apple Music is not a backup service. Be sure to back up your iOS devices, and your Mac or PC, so that you have a copy of your music and other information if your device is ever replaced, lost, or damaged.” [1]

Only the music from the iCloud Music Library will be inaccessible/will get removed, when you turn that feature off. The local files, that are not part of the subscription, should not go. Then look what is left: those black text tracks will stay. (Listings in gray, if any, will be inaccessible.)

If you turn the iCloud Music Library back on, then the previous library will be back (but possibly your subscription downloads will not).

Does that sound like a good test, before your subscription expires?

A couple days ago, I unsubscribed from Apple Music so my iCloud Music library also expired, I assume. I'd still like to have my local iTunes files on my iPhone, which wasn't a problem until I accidentally clicked "remove download" on one of the albums I wanted to have on my iPhone, resulting in it removing the local download off of my computer as well. Why does it still give me the option to remove the local download while I'm not able to retrieve those files from the cloud? The album is now sort of stuck in iCloud and I can't get it back. Is there any solution to that?

(I could redownload it because it's a mixtape but I'd like to have the correct amount of plays etc on there)