I'm totally in favor with your post, but not everyone is willing to self-host or is capable of doing it. So I recommendation would be and one that I'm currently using, is when uploading a file to these cloud services encrypt your files. I'm using #cryptomator, but I'm sure there are other alternatives, like #rclone. There is also #veracrypt, but to my understanding, is not great for cloud sync.
Cryptomator is open source and free, but only on desktop. To use the mobile version, you will have to pay. Here is a list of alternatives to cryptomator, if you are familiar with one, please share your knowledge.