Appendix's freezing last-slide-number does not work for the simple style

[kazuyanagimoto]

I think the appendix freezing last-slide-number only works for the block style but not for the simple style. Here is a small example.

And if possible, can I ask a way to manually freeze the last-slide-number, which works for the simple style?

#import "@preview/touying:0.4.2": *

#let s = themes.metropolis.register(aspect-ratio: "16-9", footer: self => self.info.institution)
#let s = (s.methods.info)(
  self: s,
  title: [Title],
  subtitle: [Subtitle],
  author: [Authors],
  date: datetime.today(),
  institution: [Institution],
)
#let (init, slides, touying-outline, alert) = utils.methods(s)
#show: init

#show strong: alert

#let (slide, empty-slide, title-slide, new-section-slide, focus-slide) = utils.slides(s)
#show: slides

= First Section

#slide[
  A slide without a title but with some *important* information.
]

// appendix by freezing last-slide-number
#let s = (s.methods.appendix)(self: s)
#let (slide,) = utils.slides(s)

= Appendix

== Appendix 1

== Appendix 2