There is a distinct difference between "client-side" menus used by players and "server-side" menus used by admins: Scripting in Lua - Cfx.re Docs
Mod menus for FiveM come in various forms, from simple player trainers to advanced administrative suites. Key functionalities typically include: FiveM Mod Menu
"Outfit stealing" from NPCs, access to custom clothes (EUP), and deep player appearance modification. There is a distinct difference between "client-side" menus