During the import of the "DATEV-Bericht/EXTF_Buchungsstapel.csv", the DATEV software throws the following warnings:

1. Die Eingabe "Lieferanten-Rechnungsnummer" im Feld "Informationsart" ist zu lang. Es wird auf "20" Stellen gekürzt. --> Beleginfo - Art 5
2. Die Eingabe "Lieferanten-Rechnungsdatum" im Feld "Informationsart" ist zu lang. Es wird auf "20" Stellen gekürzt. --> Beleginfo - Art 6
3. Die Eingabe "Subcontracting Receipt" im Feld "Informationsart" ist zu lang. Es wird auf "20" Stellen gekürzt. --> Beleginfo - Art 1
4. Die Eingabe "xyz" im Feld "Buchungstext" ist zu lang. Es wird auf "60" Stellen gekürzt.
5. Zu diesem Buchungssatz liegen OPOS-Informationen (z.B. Postensperre) vor, es ist aber kein OPOS-Konto erfasst. Die Opos-Eingaben werden in diesem Fall verworfen. --> This error is created during import when the field/column "Fälligkeit" is filled out. OPOS is "Offenen Posten" and is triggered by the "due date" (Fälligkeit). As in this case the import was for the annual closing (Jahresabschluss), this value is not relevant.
6. Das Konto 2920 ist für den Betriebsvermögensvergleich relevant. Daher ist die Zuordnung zu einer BVV-Position erforderlich. --> I think, this error is very specific and does not occur on a regular basis. It has nothing to do with the import itself.

Proposal:

1. Change "Lieferanten-Rechnungsnummer" in "Lieferant-ReNummer"
2. Change "Lieferanten-Rechnungsdatum" in "Lieferant-ReDatum"
3. Limit all "Beleginfo - Art X" to 20 characters
4. Limit field "Buchungstext" to 60 characters (Remark: already implemented, the issue came from a manual edit and utf-8 save. Datev expects latin-1.). Additionally, I would recommend to limit the "remarks"-field that fills this text to 60 characters or at least add a remark that the field will be cut of in the export.
5. Give the user an option to exclude the "Fälligkeit" during the export or at least make the user aware that this field is the reason for import errors.
6. No changes.

Key results after fixing these topic:
The import is "almost" free of warnings, the import is sucessfully and the balance and profit/loss calculation of ERPNext and in DATEV yield an identical operating result aka happy tax consultant.

Key remarks:
This does not conclude that the data in ERPNext is always correct and that the bookings made are correct. The accounting and correct assignment of accounts is key part of an accounting department and final checks and changes of the tax consultant are likely.
Additionally, the fixed assets are still an open flank and need to be inserted in DATEV manually. The calculation of depreciations in ERPNext does not match out of the box the DATEV calculation.