Rest api to get all item Item is a Record equal to yes

SharePoint uses some hidden columns to indicate if an item is a record.

Since, you have specified SharePoint online, typically, you would be setting a retention label or a compliance label to a document, hence you can check if _ComplianceTag (this is the internal name of the compliance label column) is not null or empty.

However, it is not mandatory that a compliance label when assigned to a document will convert it to a record (depends upon a setting in the compliance center).

Hence you can also check the "item is a record" column in your library, the internal name of the column is _ISRecord, and will hold a non-zero value if the item is declared as a record.

The rest url would be of the form: GET https://{site_url}/_api/web/lists/getbytitle('ListName')/Items?(Column Internal Name operator value)

refer: https://www.c-sharpcorner.com/article/sharepoint-2013-using-rest-api-selecting-filtering-sortin/