So when you are in the saves folder (Documents > Electronic Arts > The Sims 4 > saves), depending on what you want to bring over the most important files are the ones that end with ".save".
So if you want just your most recently played sims brought across just grab the most recent one. I generally will find out the name of the recent one and take the ".save" file and the other 5 files that have the same name but end with: ".save.ver(0-4)"
So my most recent save at the moment is named: "Slot_00000017.save" so I'd take that and also the version ones as well ("Slot_00000017.save.ver0", "Slot_00000017.save.ver1", "Slot_00000017.save.ver2", "Slot_00000017.save.ver3", and "Slot_00000017.save.ver4") . Each "slot" number is a different save, so when you look at the load game screen each sims family is the save. I attached a screenshot of my current saves folder where it shows the file names and types.
Just put them in the same folder on the new PC and launch the game and the saves should appear. (If I get a new PC, i just take the entire "saves" folder to the new one.) Just drag the folder into your google drive and as long as you have space it'll upload with no troubles! 🙂
I hope this helps!