As part of European data protection legislation, Apple has now introduced a way to download its data from the iCloud.
Under the link https://privacy.apple.com/ you can log in with your iCloud data and then have various options: you can completely delete your account, temporarily suspend it, correct data or download existing data. This means that the storage of user data in the iCloud in the EU complies with the law, as the free movement of data is envisaged. This means that you should be able to take your data from one provider to another. This is now possible at Apple.
If you do that, you should bring some time with you: depending on how much content you have uploaded, there are several gigabytes available for download.