Lets try this, if you don't mind.
Open Chrome, and Edge, and your drop box account, then right click the task bar, and open inormation that shows you the resource usage. Then go ahead and take a screen shot of the image that shows you the avialable resources and post it here ( not the running tasks ). Once you do that, if CPU usage is still up, please run this command :
netstat -aon | more
See if you can copy that and get a picture of that, also post it here .
try to run :
netstat -a -n -o
and get me a screenshot of that as well.
This will let me see the running processes with usage and CPU hierarchy next to them, seeing if something is getting priority it isn't. Syncing dropbox sould only cause high CPU usage IF it has a higher priority than say, windows host services, which it shouldn't.
I look forward to helping