I use google and the part number to reverse find if your model is listed.
CT2K8G4SFS824A on Google.com plus your model finds:
https://www.crucial.com/compatible-upgrade-for/acer/nitro-5-an515-54-(intel)#memory
And there it is. And if you want faster memory, Crucial lists it as well.
As I can't find any reference to 4200, I can't comment except I doubt this very much.
Hey, I have a Acer - Aspire Nitro 5 (AN515-54-xxx) laptop and I want to upgrade the ram. I found these on Amazon just want to make sure they are compatible. I read they have to be DDR4 4200 MHz but I also read it needs 4666MHz. Which one is correct? Will
these work.
https://www.amazon.ca/dp/B01BIWMWVS/ref=cm_sw_r_apa_i_2UISEb4REWHVC

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic