If stickers are already in the Frequently Used section of the emoji keyboard, they remain accessible regardless of the toggle setting. The "Send Stickers from Emoji Keyboard" option likely only takes effect when stickers are no longer in the Recent/Frequent section—essentially preventing them from reappearing or being sent directly from the emoji keyboard.
So, in practice:
- If you've recently used stickers, they'll still show up in Frequently Used and can be sent regardless of the toggle setting.
- Once those stickers are pushed out of the Frequently Used section, the toggle should start working as expected.
This behavior makes it seem like the toggle isn't doing anything at first, but it just depends on whether stickers are still lingering in the Recent History.

A workaround. If you manually remove stickers from the Stickers list, they will also disappear from the Frequently Used section of the emoji keyboard, allowing the "Send Stickers from Emoji Keyboard" toggle to take effect immediately.
How to Remove Stickers:
- Open the Messages app.
- Tap the Stickers button.
- Long-press on a sticker and look for a Remove or Delete option.
- Alternatively, go to Settings > Stickers and remove sticker packs.
Once the stickers are gone from Frequently Used, you should notice the toggle working as expected.