Restore encrypted files from broken nextcloud database

I have a backup of my files from a broken nextcloud 18 installation.
The mysql database failed at some point and i tried for weeks many ways to restore it.
now i have given up and reinstalled an other nextcloud.
i copied the old files of a user who did lost some files because he did not keep them all on his computer.
But all i have are the encrypted files, and the private and public keys in the folder
files_encryption/OC_DEFAULT_MODULE

how could i restore these files ?