The Bug:

The sounds of end portals opening aren't controlled by the correct sound slider and are instead controlled by the "Hostile Creatures" sound slider. This seems illogical as end portals aren't associated with hostile creatures of any kind.

Steps to Reproduce:

1. Navigate to the "Music & Sounds" settings menu.
2. Turn the "Hostile Creatures" sound slider to "OFF".
3. Turn every other sound slider to "100%".
4. Exit this menu, and construct an end portal.
5. Listen closely as the end portal opens.
6. Take note as to whether or not the sounds of end portals opening can be heard, (are controlled by the "Hostile Creatures" sound slider).

Observed Behavior:

The sound is controlled by the "Hostile Creatures" sound slider.

Expected Behavior:

The sound would be controlled by some other sound slider and not the "Hostile Creatures" sound slider. In this particular scenario, the "Blocks" slider would work nicely.

Code Analysis:

Code analysis by Avoma can be found below.

The following is based on a decompiled version of Minecraft 1.18.1 using MCP-Reborn.

...
this.level.playLocalSound(d4, d5, d6, SoundEvents.END_PORTAL_SPAWN, SoundSource.HOSTILE, 1.0F, 1.0F, false);
...

If we look at the above class, we can see that the sounds of end portals opening are sourced from SoundSource.HOSTILE, otherwise known as the "Hostile Creatures" sound slider.