I' lost twrp and magisk this time which was annoying, but fixable. My main concern is about the partitions which don't show up in twrp (but files are all there in OP's file manager) and which twrp can't repair. I've no idea if the installation process will crash because of this (boot loop etc).
I suppose I really should have done a clean install for Android 10, but I never trust the backup processes. And now I can't use the OnePlus app to copy over my my 5T because Bluetooth won't work (though I have copied the backup to my pc).