Kobo sync in grimmory requires adjustment of the sync url.
Get token from Grimmory in Settings → Devices → Kobo sync token
Connect kobo to PC and select connect on Kobo
edit .kobo/Kobo/Kobo eReader.conf file and adjust the following variables with your url and sync token
api_endpoint=https://grimmory.xxxxxx.org/api/kobo/f0a85d92-xxxxxx
image_host=https://grimmory.xxxxxx.org
image_url_quality_template=https://grimmory.xxxxxx.org/api/kobo/f0a85d92-xxxxxx/v1/books/{ImageId}/thumbnail/{Width}/{Height}/{Quality}/{IsGreyscale}/image.jpg
image_url_template=https://grimmory.xxxxxx.org/api/kobo/f0a85d92-xxxxxx/v1/books/{ImageId}/thumbnail/{Width}/{Height}/false/image.jpg
user_ratings=https://grimmory.xxxxxx.org/api/kobo/f0a85d92-xxxxxx/v1/products/{ProductId}/rating/{Rating}
enable “Convert to KEPUB” for two way reading sync to work