There is no such concept in Mautic as Leads vs. Contacts. All are “contacts”.
Don’t worry it’s all handled pretty well.
Leads in SuiteCRM - > Contact in Mautic
Contacts in SuiteCRM → Contact in Mautic
Contact in Mautic → Lead in SuiteCRM.
It matches on email address as a unique identifier so there are not duplicates.
If you convert a lead to a contact in SuiteCRM Mautic handles that by overriding the lead with the contact.
It all works very smoothly. The only issue you run into is if you have leads or contacts with a blank email. Then you have problems because there is no unique identifier. This will create many duplicate contacts in Mautic as it treats each as unique on every sync.
What I do in order to keep it straight, because sometimes you want campaigns going to just leads or just contacts, is I sync the lead status (I also ensure all contacts have a lead status of converted). Then if I need to segregate leads vs contacts in Mautic I just filter on converted vs. not converted.