Do you have specific data that youd like to bring under your control? Any specific services youd like to turn off?
We ask mainly because the self hosting stuff is full of technical detail, how to guides and can be quite overwhelming initially...
NextCloud is a great choice that gives a good basis and starting point for breaking free of other providers. For our project we recommend NextCloud over other options to our users.
The list @Are0h
posted is also good, we see more than a few great projects listed there. Just be mindful some projects we saw on the list are defunkt/generally dead.