Because it runs as a separate process and only reads/writes to memory rather than "hooking" into the game, it is famously resilient to Rockstar's anti-cheat updates.
Version 0.9.4 was specifically released to address compatibility with certain GTA Online updates. Users often report that if a menu version doesn't match the current game build, it simply won't open or may cause the game to crash.
Modding in online games typically violates Terms of Service and can result in permanent account bans. modest-menu_v0.9.3.zip - UnKnoWnCheaTs