iPhone X RAM missing?

A few years ago (2-3 years ago) I broke my iPhone Xs' screen so I went and got it fixed at some 3rd party shop. Screen wasn't great and it glitched every now and then but that's not why I'm here. Ever since, I noticed that it was slower than usual but I just blamed it on the age of the phone, I didn't think much of it. Safari takes ages to run and load pages even when my Wi-Fi is great. I've had to use Chrome because of its better optimization. I've had this program called Phone Doctor (off the App Store) downloaded for quite a while now but I haven't used it. I just realized though, that it says that I have 2.8 GB of RAM in total. The iPhone X is supposed to have 8 GB (like all iPhones). Is it possible that the repair shop exchanged the 8 GB for 2.8 GB of RAM for an extra buck? My RAM usage never goes lower than 90%. It just cycles from 90-99%. The same program also says that my CPU is under absolutely no pressure. My phone is just in a constant bottleneck.

If this is true, I'm not looking to fix it. I'll just get a newer phone at this point.

Could you guys maybe suggest another program that might further prove this if necessary?

PS: I just realized that it has 3 GB, rendering my whole argument useless. Could someone please explain the CPU to RAM usage ratio though?