Sequoia latest update wreaking havoc on system

I have just updated my otherwise trusty Mac computer to Sequoia 15.0.1, and am now dealing with a host of new problems right and left on my system. Can you help?

The most glaring symptom is that immediately after the 15.0.1 update, half of my computer's screen became "grayed over" — that is, covered with a block of horizontal lines that did not exist before the update. The block of lines move up and down slightly and flicker a bit.

Please see attached screenshot for details. (I did try taking a screenshot directly from my Mac internally, but this block of horizontal lines does not appear at all on the computer's own internal screenshots. Thus, my taking of this photo with my iPhone externally.)

The block of lines you see in the screenshot do not seem to be interfering with the actual functioning of the computer — I can still do tasks on my Mac computer "under" the block of horizontal lines. But this is definitely not normal and I need to resolve this major problem.

There are a host of other side issues I am trying to deal with as well, like plugging up leaks in a sinking boat: a noticeable lag in the computer's operation, network connection issues, Time Machine backup issues and even the inability to run Apple diagnostics or enter into safe mode online. They all started up right after updating to Sequoia 15.0.1.

What could be the problem here with the display/screen and how can I begin to fix this? Desperately in search of answers here.