Error migrating to sqlite backend

[Axel Braun]

Hi,
I wanted to give the migration from Postgres to sqlite another try
KMail is 26.08.1 on openSUSE Tumbleweed
When running
I ran 
akonadictl fsck
akonadictl vaccum

before

 akonadi-db-migrator --newengine sqlite

During this I get the error:
org.kde.pim.akonadiserver: DATABASE ERROR while PREPARING QUERY:
org.kde.pim.akonadiserver:   Error code: "42703"
org.kde.pim.akonadiserver:   DB error:  "ERROR:  column \"pimitemflagrelation\" of relation \"pimitemflagrelation\" does not exist\nZEILE 1: UPDATE PimItemFlagRelation SET PimItemFlagRelation.Flag_id =...\n                                        ^\nTIP:  SET target columns cannot be qualified with the relation name.\n(42703)"

I tried gemini to find a solution, but except some dangerous proposals like
mv ~/.local/share/akonadi ~/.local/share/akonadi.bak
(which deletes all local content) nothing useful found.

Any hints to fix this?
Thanks
Axel