the HTML Anchor field is a core WordPress field, you will find it for ( almost ) every Block you add to a page.
Whatever value you add in that field will get output to the
ID attribute of the blocks HTML.
<div id="my-html-anchor-field-value" class="gb-container ....">
ID attribute CANNOT contain a
# – its invalid HTML.
There are a few reasons for this, but the main on is because the
# is used as an general identifier when you for example:
a) reference the ID in a
href attribute eg.
<a href="#my-html-anchor-field-value">My anchor link</a>
b) use it it in a CSS selector hook eg.
So don’t add the
# to that field.
You add the
# when you want to reference the HTML element with that ID.