I am having the same issue, it should be a bug as I don't have this issue when I am previewing the same file in VS Code.

It's been three months since this question was created, could someone from Github help here?

I'm having the same issue. i.e.

This works when the Alert is at the beginning of line:

1. Title of first section

   This is the first section.

This doesn't work, when I try to align with another paragraph by adding three spaces in front of the line:

1. Title of first section

   This is the first section.

   [!NOTE]
   This is a note that creates a quoted text. It doesn't create the Alert icon.

The documentation for alerts does state:

Alerts cannot be nested within other elements.

I agree with @kasir-barati that this restriction should be considered further because it severely limits the utility of alerts.

👍 ing and adding my use case: a Note admonition associated with an item in a bulleted list. Example:

1. Here's a thing
    ```
    with.some(code)
    ```
    > [!NOTE] 
    > The variable code is defined in foo.bar
1. Next, frogblast the vent cores

But the admonition renders as a block quote due to 4 spaces required to keep the bulleted list going:

1. Here's a thing

   with.some(code)
   

   [!NOTE]
   The variable code is defined in foo.bar

2. Next, frogblast the vent cores

You can elide the four spaces and the admonition will render correctly, but the bulleted list will not continue:

1. Here's a thing

   with.some(code)
   

1. Next, frogblast the vent cores

You can manually change the numbers, but of course that relies on users noticing and correcting the problem, which in practice doesn't happen as often as you'd like

Another use case is an alert inside a <details> block:

Example

<details>
<summary>Click to expand</summary>

Other _Markdown_ elements work.

> [!NOTE]
> But an alert does not work since it is "nested", even though it is not indented.

</details>

Result

I'd like to upvote this issue – I also found all the use cases mentioned above quite problematic, since alert panels nested within a bulleted list are not a rare use case. It would be super cool if you could extend it 🙏🏻

Sadly this is still unanswered

I'd love to see GitHub reconsider the current state of not allowing Alerts to be nested inside of other elements. Having to keep Alerts (which I love) outside of collapsible content makes for very ugly and inconsistent-looking documentation.

Please consider adding the ability to nest Alerts inside of other elements!

Indented Alerts work fine on GitLab, would be nice if GitHub can fix this problem.

Like many others before me, I'm here to express my support of this issue.