Thanks for your feedback.
Before the job runs, the value of github.job is always empty. Only when the job is actually running, we can get the job context. If you are using this if conditional in jobs level, the value of github.job is always empty. So no matter what, your job will not be skipped. This is why you can not use if conditional at jobs level. Please use the if conditional in steps level. For example:

on:
  workflow_dispatch:
    inputs:
      jobs:
jobs:

build:

runs-on: ubuntu-latest
steps:
  - name: test 
    if: ${{ github.event.inputs.jobs == '' || contains(github.event.inputs.jobs, github.job)}}
    run: echo Github current job [${{ github.job }}]

This is why you can not use if conditional at jobs level.

But it’s supposed to be supported, right? This problem seems to still be occurring, and I cannot find anything about the impossibility of using github.jobs in the jobs’ if context.