Hi @ligui ! As you are new to the community, when you get a chance, please introduce yourself here.
I’d also encourage you to add a real picture as your avatar because it helps build community!
ODK-X has sub-forms, which are similar to repeat groups, and can be used for longitudinal data. You can query across forms to link data using linked tables.
The longitudinal clinic app: Longitudinal Clinic Study App — ODK-X Docs is a good example
And the documentation for linked tables is here: Using ODK-X XLSX Converter — ODK-X Docs