The syntax highlighting for shell scripts broke in vim 9.0. A suggested solution is to downgrade to 8.2 but that is problematic since there is a runtime dependency, and it will be fixed in the next release anyway.
I’m just posting to document the workaround I discovered in case anyone else is annoyed by this.
There was discussion here: https://vi.stackexchange.com/questions/40208/syntax-highlighting-for-shell-scripts-broken
That pointed to a thread on the vim google group, and this solution was posted: sh/bash highlight broken since upgrade of sh.vim version 205 · Issue #11937 · vim/vim · GitHub
That worked for me as an interim fix until the package is updated.