I'm literally asking for a friend, who has a MacBook Pro 2016-2017 with no touch bar. (Big Sur 11.4, updated about 2 months ago).
They report that recently (noticed within the last week) when the laptop gets hot, usually when driving a very large BenQ monitor or perhaps when doing intensive numerical calculations, single pixel tall black lines appear across the bottom of the laptop's monitor in the Dock area. As the laptop continues to get hot over a period of 10 to 20 minutes, more isolated lines appear.
Their research shows that it appears to be a known problem with this model, and may be associated with something called a "T-CON" board.
Before considering a major repair, one bit of advice in this and this answer is to investigate the fan speed; is it going to full speed soon enough, does something need to be reset, etc. It also links to
Question: Is it possible to check the current speed of the fan on a 2016-2017 MacBook Pro? If that suggests it's not running fast when the computer is hot, is "resetting the SMC of your Mac" at least a safe thing to try?