Hi @Miron Luca Ferreira Rodrigues
Thank you for posting your question on Microsoft Q&A.
I understand that you want to remove a user's integration from on-premises AD and Azure AD Connect.
To do this, you can move the user in on-premises AD to a non-sync OU and run a sync on AD Connect. Non-sync users are not synced to Azure AD Connect, so the user will not be available in sync and will not be able to access any SSPR or any configuration that you have done in on-premises.
However, even if you remove the user from Azure AD Connect, you cannot edit the user's properties from Azure cloud because the user is still part of on-premises AD. Unfortunately, converting a synced user object to a cloud-only object is still not supported at this time. The only method to convert a synced object to cloud-only is to disable directory synchronization, but this action will convert all synced objects. To achieve your goal, you will need to create a new user in Azure cloud.
Hope this helps. Do let us know if you any further queries.
Thanks,
Navya.
If this answers your query, do click Accept Answer
and Yes
for was this answer helpful. And, if you have any further query do let us know.