But better be safe than figuring out later you actually do.

But I never died before so what could possibly go wrong?

I’m using a combination of iCloud and Syncthing. iOS syncs to my Mac with iCloud and Syncthing picks it up from there. For me it was about having a second copy, that I completely control, and not so much about getting rid of all Cloud services there. If, however, Syncthing could get into the depths of iOS file system, I would consider getting rid of iCloud.