Multiple horizontal line of pixels not functioning properly

Oftentimes these are symptoms of a damaged display assembly. This series has a weakness within its design as the temperature sensitive T-CON board is held within the uppercase unlike the older 2015 systems which had it within the much cooler lid space. The reason is space! Apple just went too far with their Thin Is In mind set. Here Intel & AMD failed to express the needed cooling for there chips given what the market was going to do with these systems.

So you’ll need to think through is the cost of replacing the display worth it MacBook Pro 16" 2021 Screen Replacement

The last issue here is over time the fans and heatsink fins get clogged up with junk lowering there ability to cool. You do need to clean the internals at least bi-yearly and make sure you don’t use your system on soft surfaces as these tend to choke off the vents and there fluff is the worse in clogging up the system. At least do this ASAP! Get a small soft paint brush and a can of can’d air carefully dust the case and logic board. Take the fans out so they can be cleaned and so you can reach the heatsink fins again carefully scrub down the blades and fins. Use the can’d air to blow the now loosened junk using short blasts.

I strongly recommend installing a good thermal monitoring app and one that can push the fans when things get to toasty this is what I use in my systems TG-Pro