As @ku4hx mentions, this laptop runs hot...you do have an i9 CPU which runs extremely hot....much hotter than an i7. I don't think Apple should ever have used an i9 CPU in this laptop since an i7 runs hot enough as it is.
Netflix can easily heat up a laptop since it will be using the CPU & GPU to stream HD content.
Make sure you are not running any anti-virus apps, cleaning/optimizer apps, or third party security software since they are not needed on a Mac and usually causes more problems than they solve. Plus these types of apps tend to cause a computer to work harder which make it run hotter because these types of apps interfere with the normal operation of macOS.
You can run the Apple Diagnostics to see if any hardware issues are detected.
You can also try booting the laptop into Safe Mode to see how the laptop performs. If the laptop performs better while booted into Safe Mode, then it most likely means you have some third party software installed which is causing the problem. The most likely culprits are the ones I mentioned previously. You can always run EtreCheck and post the report here so we can examine it for clues...just make sure to use the laptop normally and wait until you experience the issue before running EtreCheck so the report may have a clue show up in the performance metrics section of the report.
Make sure to disconnect all external devices in case one of them is causing a problem.
You can try an SMC Reset and PRAM Reset (the PRAM Reset is unlikely to do anything for this issue).