Here's the relevant paragraph from the IRS publication which clarifies what to do with a Box 20 Code AG "Gross receipts for section 448 (c)".

Instructions for Form 1065 (2023)
U.S. Return of Partnership Income

https://www.irs.gov/instructions/i1065#en_US_2021_publink100016024

"Gross receipts for section 448(c) (code AG). Regulations section 1.163(j)-2(d)(2)(iii) requires that partners in a partnership include a share of partnership gross receipts in proportion to their share of gross income under section 703 (unless the partnership is treated as one person under the aggregation rules of section 448(c)). Partnerships with current year gross receipts (defined in Regulations section 1.448-1T(f)(2)(iv)) greater than $5 million are required to report to partners their distributive shares of their current year gross receipts, as well as their distributive shares of gross receipts for the 3 immediately preceding tax years. If a partnership and a partner are treated as a single employer under the section 448(c) aggregation rules, and the partnership has current year gross receipts greater than $5 million, then the partnership should also report its current year total gross receipts, as well as its total gross receipts for the 3 immediately preceding tax years, to that partner. See
IRS.gov/newsroom/ faqs-regarding-the-aggregation-rules-under-section-448c2–that-apply-to-the-section-[product key removed]ess-exemption. Partnerships whose current year gross receipts are less than or equal to $5 million may also use this code to report gross receipts."