ModernFix stopped working? In 90% of cases it's one of three things: wrong mod loader, outdated version, or a conflict with another mod.
1) Update ModernFix to the latest version. 2) Check you're using the right loader (Fabric vs Forge). 3) Remove recently added mods one by one to find the conflict.
Delete the old .jar, download the fresh copy and reinstall. The installer handles this automatically.
Related: Home (/), 1.20.1 (/1.20.1/), 1.19.2 (/1.19.2/), 1.18.2 (/1.18.2/), 1.16.5 (/1.16.5/)