How can I install and use mpv-autosubsync-git?

Yes I have. But it doesn’t really solve the issue, it only installs a different file. The PKGBUILD only installs the file autosubsync.lua when it should install all this files

Make sure autosubsync-mpv is installed properly. This is the expected content of your ~/.config/mpv/ directory:

|-- script-opts
|   `-- autosubsync.conf
` -- scripts
    ` -- autosubsync
        |-- autosubsync.lua
        |-- main.lua
        ` -- menu.lua