Hello,
Thank you for posting in Q&A forum.
Normally, enabling hybrid Azure AD joining will not cause any prompts or issues to the end users of existing computers that only join the AD domain. This process is mainly to connect these computers to Azure AD, in order to facilitate the functionality and management advantages of Azure AD. The end user should be able to continue using the computer normally without receiving too much interference or prompts.
Hope this answer can help you well.
Best regards,
Jill Zhou