Thank you very much
In the meanwhile I came to the same conclusion by reading a tutorial online
It seems the best way would have been to use to One Plus switch app as long as it worked or a software calle Wondershare Mobile Transfer but it requires pc installation which right now I can't do
The other way is indeed backing up everything on Google Drive with the Ios version of the Google Drive app and then importing everything on Android. The only drawback is that it's slower but it should do the job