Acer nitro 5 AN515-58 CPU throttling I notice high CPU temperatures and fps drops

You have done all that a consumer can do as a user but, your laptop if it reaches its critical temps at the cpu or gpu will automatically turn off to stop any damage to the laptops components. Also and with games like Fortnite and Rocket League there are other tweaks and many links like this for >>> Fortnite and also patches that you should install which will improve Fortnite and Rocket League playability, so check all those out as your laptop is setup as a general gaming rig and needs allot of different settings for each gamed.

Also, be very careful as your laptop is under Acer 12 months warranty and I wouldn't open it and/or do anything to a new laptop like yours, as it could void your warranty, especially if you open it and damage the case and internal components that could short out from static etc etc

There are many solutions to throttling and high temps in a laptop, so contact Acer in your area and tell them the throttling problems that you are having as high temps are common in many laptops while gaming, as all laptops have restricted cooling and the cooling can't be improved like in desktops, except by either repasting the cpu/gpu with the top and latest solution like liquid metal paste and/or buying or building a high end tablet cooler to reduce and disperse the laptops temps.

Note: be very careful with any Liquid Metal Pastes (as they are a conductive paste) and if you apply too much of this paste, it will leak onto surrounding circuitries around the cpu and gpu of your motherboard and it will damage your motherboard beyond repair, so follow the manufacturers exact application guides to be safe and for this excellent temp reducing paste to work properly.