Misago/misago/admin/src/validation.js

const initValidation = () => {
  // js workaround for validation states
  const controls =  document.querySelectorAll(".form-group.has-error")
  controls.forEach((control) => {
    const inputs = control.querySelectorAll(".form-control")
    inputs.forEach((input) => {
      input.classList.add("is-invalid")
    })
  })
}

export default initValidation