https://fam.state.gov/fam/09FAM/09FAM030211.html
9 FAM 302.11-3(B)(1)(b)(2):
b. (U) DHS has interpreted "period of stay authorized by the Secretary of Homeland Security," as used in this context, to include:
(2) For individuals inspected and admitted for "duration of status" (DOS), any period of presence in the United States, unless DHS, an IJ, or the BIA makes a formal finding of a status violation, in which case unlawful presence will only being to accrue the day after the formal finding is made;
9 FAM 302.11-3(B)(1)(d):
For persons who have been admitted for duration of status (DOS) (as is usually the case with individuals in A, G, F, J, and I visa status), unlawful presence will not accrue unless DHS, IJ, or the BIA finds a status violation in the context of a request for an immigration benefit or during removal proceedings. This finding of status violation by the DHS, an IJ, or the BIA will cause a period of "unlawful presence" to begin. In DOS cases where DHS or an IJ or the BIA makes a formal status violation finding, the individual begins accruing unlawful presence on the day after the finding (i.e., the date the finding was published /communicated). For example, if an applicant presents a letter from DHS dated December 1, 2008, that says the applicant was out of status starting on May 28, 2001, the applicant began to accrue unlawful presence as of December 2, 2008, not May 28, 2001.
In fact I'm not sure if the 2018 policy ever applied to the DOS but I suspect that it did because it's up to DHS to define what is and isn't unlawful presence. Moreover the bars don't trigger until after departure which would create a weird scenario where literally the only people who the DHS memo would apply to would be those who'd fall out of the F-1 status, depart, and then return to US legally somehow (e.g. via 212(d)(3) waiver).