I think Enpass 6 supports importing the data only the latest version of 1Password (probably v7 not v4). Why don't you try installing the older version of Enpass and then try importing 1password data and later on you can take the backup of Enpass 5 data and restore into Enpass 6? https://www.enpass.io/support/where-can-i-download-older-version-of-enpass/