Here is a good high level video on /e/ in my opinion. The concern on this thread regarding personal data in /e/'s cloud services starts at about 3 minutes 55 seconds. When you use /e/ you are not forced to use their cloud.
Where your data goes depends on self education and learning, it is completely subjective. What is right for me will not be right for you. A couple resources to learn about to help:
-/e/'s own cloud, it isn’t end to end encrypted (E2EE) yet but it is on the roadmap. If this worries you maybe consider one that is E2EE, MEGA or pCloud Crypto (pay extra for client-side encryption drive, main drive is server side encrypted similar to /e/'s currently), or Cryptomator preupload.
-Reading at PrivacyTools, Mike Kuketz, EFF, and searching the forum here.