The jfx in the repo is 17 - that is how it is.
Being a Manjaro user for as long as two years - you know the caveats of custom scripts from AUR.
- switch to Manjaro unstable branch (on par with Arch)
- do not sync system and custom AUR scripts in the same transaction
Use a helper script to inform of updates to AUR script.
jfx 21 is a custom script found in AUR