This is what MS Copilot suggests sous condition means in this context:
In the context of a 17th-century French baptism, "sous condition" means conditionally baptised. This term was used when there was uncertainty about the validity of a previous baptism. For example, if there was doubt whether the initial baptism was performed correctly, the priest would perform a conditional baptism to ensure the child was properly baptised.
This practice was particularly important in cases where the child was in danger of death or if the initial baptism was done by someone other than a priest, such as a midwife. The conditional baptism would include a phrase like, "If you are not yet baptised, I baptise you in the name of the Father, and of the Son, and of the Holy Spirit".
