Desktop Mac with Lightroom Classic vs starting over with LR Classic?

There is no software "Lightroom Classic CC". There is Lightroom Classic (with the LrC icon) and Lightroom (with the Lr icon). Using the correct names in your discussion would be helpful.

Lightroom, which stores your photos in the cloud (or optionally on your hard disk, a new feature) does not assume mobile use, it works properly on your desktop or laptop computer (it if meets the specs), and you can also use mobile devices to edit and manage your photos.

but I DO NOT WANT MY IMAGES STORED ON ADOBE CLOUD

Then use Lightroom Classic. Do not use Lightroom. (Or use the new feature of Lightroom which allows you to store photos on your hard drive).

What happens to your photos if your remove the Lightroom Classic? Nothing, the photos are stored on your computer's hard disk, they are still there. But edits performed and other work done in LrC is gone. Better, you should leave LrC on your computer to access this work, even if you end the subscription (is that really what you are asking about?) you can still access your edits and other work.

Why do linear gradients NEVER WORK like I see in Adobe videos?

They work properly for me. We don't know the exact steps you used, so we cannot answer your question. Please give us detailed, step-by-step description of what you are doing, leaving nothing out.

About these two questions:

If I remove Lightroom Classic- what will happen to my images?

By @Kesata13

Nothing happens to the original images, because Lightroom Classic only catalogs images where they are on your own local storage, and doesn’t hide them away or upload them. So Lightroom Classic can be deleted and the original images stay where they are, with you, so you can go on to use some other application to edit your photos if you want.

If you uninstall Lightroom Classic and don’t delete the catalog(s), your edits for the image files are still in the catalog(s) on your computer and can be restored if Lightroom Classic is reinstalled.

If you uninstall Lightroom Classic and delete the catalog(s), but you also saved image edits and metadata to XMP sidecar files, other applications can use the XMP files to read metadata you entered such as keywords and captions. However, image edits will only be transferable to a few applications, mostly by Adobe, that understand Adobe-specific photo editing features.

If I install Lightroom Classic CC: what will happen to my images?

By @Kesata13

Do you mean cloud Lightroom, not Lightroom Classic? If so, you could browse and edits images on your local storage using the Local tab, but cloud Lightroom is really designed to try and upload everything you import to Adobe servers.

In other words, if like you said, you never want images uploaded to Adobe cloud servers, just don’t install cloud Lightroom. Only install Lightroom Classic, which is designed for photos on local storage. Lightroom Classic can’t even sync originals to the cloud. It can only sync lower resolution Smart Previews of local originals, and it won’t even do that by default, only if you specifically tell it to sync specific images.

Regarding the gradients question, I don’t know. I absolutely love using the masking tools, they are a godsend and in many (but not all) ways superior to the current masks in Photoshop, faster and more flexible for so many things.

I've moved this from the Using the Community forum (which is the forum for issues using the forums) to the Lightroom forum so that proper help can be offered.

Scroll down here to see a list of the forums:
https://community.adobe.com/