There can be multiple sources.
First thing first, the devs packaged the game with full encryption mode - that means not just asset index but the rawdata all encrypted, which undermines and essentially breaks UE4's ability to efficiently stream resources from PAK files, since it can't do it with pin-point precision and has to decrypt a lot of stuff on top of what's needed. This puts load on your CPU and RAM requirements. More than that, they also recently enabled gzip compression of the PAK, which adds additional cost on CPU when decompressing assets.
CPU time is requires to decrypt and decompress asset data EACH time it needs to be read from disk. It goes into system memory and then via PICEx bus uploaded into VRAM on GPU. Depending on your specs and game options (quality level) it is possible you might be limited by RAM/VRAM.
You can use stuff like Process Explorer to get nice graphs and more insight into how much resources process uses. Observe what happens from the moment when you load into the game.
Additionally, use HWInfo to get summary of your specs.
My first recommendation is to lower all setting to minimum.
And to be clear, I have experience in this field more ways than one, so instead of having a case of big brain gone empty.
since you wanna try me here,
I suggest starting with this, seems more your speed.
Coursera pretty much just offers classes online. Some of them are full uni classes, some of them are more introductory or like intensives. The majority are taught/made by college professors though. I've taken a couple of their classes in the past for intro coding stuff. In general the class is free (not always), but if you want the certification (for resume/transfer credit/etc) you have to pay. For this specific class both are free and, namely they are waving the certification fee and offering it completely for free.
Here is a list of stuff they made free to make self isolation stuff easier/productive: https://www.freecodecamp.org/news/coronavirus-coursera-free-certificate/