How to disable toasts (popups)? An example of grey and white note that I mean is, like when you copy something, a small grey background and white lettered bubble appears for a few moments saying 'copied to clipboard'. My phone has some sort of malfunction where it dispays that prompt for several minutes at a time. Very annoying.
How do I disable that?
I am using a Samsung Galaxy S9.
First of all...
What you refer to as grey and white notes are officially named Toasts.
Toasts are one of Android's built-in ways to output info/feedback to the user.
Toasts can be shown by:

The Android OS
System apps
User installed apps
Background services
etc..


Second...
You gave almost no information that is useful for troubleshooting your problem.
This is why I'll assume you just want all toasts disabled.

However...
Disabling Toasts on a system-wide basis is not easy. It may even be impossible  without rooting your phone (unlocking permissions) and subsequently changing part of the system software.

And last...
Improving your question to include more info would make more helpfull answers possible.
Useful info would be:

If all or only some toasts misbehave.
If not all, then which ones specifically.
What they say.
If this happens every time, randomly, at specific times, etc.
When did it start happening?
Did you install something fishy?
Do you know/can you guess which app they belong to?

Relevant info

Popups, dialogs, notifications, toasts: what's the difference?
Toasts overview | Android Developers