Try moving the convert statement after the comparison.
index="xxx"
| rename "logs{}.*" as *
|fields user.lastName,projectId,user.firstName, user.lastName,time,type,date
| eval acteur='user.firstName'." ".'user.lastName' | search acteur="AAA"
|rename projectId as NOVA_ID | join[ search index="gtav2_projects" projects{}.icma="*"
|rename projects{}.id as NOVA_ID, projects{}.icma as ICMA ]
| rename projects{}.title as Title ,projects{}.client.name as "Nom Client"
| dedup Title |eval dateLimite =relative_time(now(),"-7mon")
| where date > dateLimite | convert timeformat="%d/%m/%Y %H:%M" ctime(dateLimite)
|table "Nom Client",Title,ICMA,date, dateLimite, NOVA_ID
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