I have moved twice now. First from my raspberry pi to cloud and the second time between cloud providers. There might be other ways but you can share folders be

I have moved twice now. First from my raspberry pi to cloud and the second time between cloud providers. There might be other ways but you can share folders between Nextcloud instances. I have shared my whole nextcloud from the old one to a folder in the new one. Then in the new instance you copy folders from the shared drive to your new instance. For ~300-400 GB in takes a moment and I do some spot checks, but after half a day it's done. And you don't actually do things, you just wait that a folder copy finishes, check and then start the new one. There might be more automated ways, but this worked for me.