MarsSeed [1] filed a deletion request for avxsynth-plugin-decomb [2]:

It is useless to keep this broken, EOL plugin from 12 years ago a
decade ago, as avxsynth itself is not compatible with current
libraries, and is itself EOL since 9 years ago.

Successor of the latter is avisynthplus, available from Arch repo.

[1] https://aur.archlinux.org/account/MarsSeed/
[2] https://aur.archlinux.org/pkgbase/avxsynth-plugin-decomb/