Loaders define the environment
A mod file targets a particular environment and game version. Placebo's official project lists Forge and NeoForge files. Do not infer that a jar works on another loader merely because both run Minecraft Java Edition or have similar version labels.
Do not mix incompatible files
Use the loader tag on the actual download. A Fabric or Quilt pack should use mods designed for that environment; placing Forge or NeoForge jars into it does not provide a normal supported installation. Check every dependent mod before considering a loader change.
Migrate through a new instance
If you decide to change loaders, create a separate profile and rebuild a compatible mod list. Preserve the old instance and world backups. Confirm that your content mods exist for the new environment before opening a valuable world, since missing content can affect saves.