Reloading resource packs no longer shows the progress bar while the transparent background is shown

The bug

In previous versions, when reloading resource packs by pressing F3 + T, a progress bar would appear while the transparent red screen was shown. This is no longer the case in 21w10a. Now, the progress bar is only shown when the solid red screen is displayed.

Videos are attached from 21w08b and 21w10a.

How to reproduce

1. Reload resource packs by pressing F3 + T, in 21w08b or earlier
   ✔ A progress bar is shown while the background is transparent

2. Reload resource packs by pressing F3 + T, in 21w10a
   ❌ No progress bar is shown while the background is transparent