Use case for this in core is the "Number of items to index during cron runs" setting in admin/config/search/settings:

It currently allows for a choice between 6 pre-defined values, as shown in the screenshot above. Ideally, we could allow any custom value (grater than 0), and offer these values as suggestions, instead of having them hard-coded.
The HTML5 number field allows that as follows:
<input id="ticketNum" type="number" name="ticketNum" list="defaultNumbers">
<span class="validity"></span>
<datalist id="defaultNumbers">
<option value="10045678">
<option value="103421">
<option value="11111111">
<option value="12345678">
<option value="12999922">
</datalist>
Which makes the <input> field a free-type number field + offers the suggested values in a drop-down in the same field:

Recent comments
Please can you provide more information about the use case for this and also a screenshot or mockup of what you are trying to achieve. There is a request here (https://github.com/backdrop-...
How can I display the username or user profile picture in the menu?
Oh thanx ! I had an "old" text format that I had disabled. I re-enabled this format in the field body with the permissions and the field comes back for editing.
Problem of access to the body field with a simple post
See https://github.com/backdrop/backdrop-issues/issues/7148
Problem of access to the body field with a simple post