How do I use REGEXTRACT to return grouped numbers from a string where the number of groups varies?

In Google Sheets, I'm trying to return numbers from within a text string.

The numbers are values of the property named either item_id or item_ids.

I've tried the REGEXTRACT function but I'm struggling.

Example 1

1.   Text in cell A1

   <!-- wp:shortcode -->[aces-unit-1 item_id=""1236""]<!-- /wp:shortcode -->

2.   Expected Result

   1236

Example 2

1.   Text in cell A1

   <!-- wp:shortcode -->[aces-bonuses-1 items_number=""4"" external_link=""1"" category="""" items_id=""1563, 2372, 3855, 3980"" exclude_id="""" parent_id="""" columns=""4"" order="""" orderby="""" title=""""]<!-- /wp:shortcode -->

2.   Expected Result

   1563, 2372, 3855, 3980