BTW, Many years ago I saw Reb Elchonon’s tshuvah on secular studies, and I don’t think he assured it, provided 3 conditions were fulfilled.
1) No mixing of genders
2) No mixing with gentiles
3) No apikursis
I believe that most yeshivas today meet those requirements, and therefore it is not a problem.
However, it has been a long time since I saw it inside, so if anybody has a copy, please correct.