Nc 20.010 backup - restore in 21.x

i want to restore a backup from version 20.010 to nc 21.x
is there any howto , faq how to proceed ?

Normally, you restore the same version. If it’s the next major version, you can copy the code of the new NC version (NC 21.x) code and put your old data (data folder, database content, config.php file). Then you have to run the occ upgrade command to execute the upgrade.