Pre-pandemic, AA 3-class transcon J and F pax could get into respective OneWorld lounges. I haven't tried since OW reopened but I don't see why it would be any different. Some people were denied entry incorrectly by poorly trained lounge employee but the entry rules were clearly stated - if you can get in AA lounge based on class of service (e.g. transcon 3-class J), you can get in OW lounge. Membership/elite status entry is different... those follow OW rules so AA elite (and now AS elite) on domestic flights are not allowed entry based on status.
BTW, I was back in Flagship lounge yesterday for the first time since it reopened... was nearly empty when I was there (7AM).