Various achronim discuss whether women are obligated in the mitzvah of tosefes yom tov. A nice lomdish formulation of the question (which was discussed here before) was posed by a questioner to R’ Binyamin Zilber (Az Nidbiru vol 1): if tosefes yom tov is an extension of kedushas yom tov itself, then just as women are obligated in the mitzvos of yom tov, they are obligated in tosefes, but if tosefes is an independent mitzvah, then there is no source to obligate women.
While the lomdus sounds nice, the assumption behind it is questionable. Although the gemara explicitly states that women are obligated in tosefes yom hakippurim, there is no source that would indicate an obligation in tosefes yom vov. Recall Tosfos (Kiddushin 34) from yesterday’s post suggested in their question that women are exempt from the aseh of yom tov, and retracted that assumption only because the aseh is attached to a lav. Tosefes yom tov is not attached to any lav, and so the exemption of women should stand. (This of course begs the question of why tosefes y”k is different than tosefes y”t).
Daf Yomi learners, however, will recall Tosfos (Kesubos 47a d”h d’masar) which writes that women may not do work during the tosefes shabbos, indicating that they are chayavos. The Ksav Sofer (O.C. 56) suggests that perhaps women are exempt only from zman gerama mitzvos like tefillin, which demand a kum v’aseh action to perform; they are, however, obligated in issurei aseh, such as the aseh of yom tov, which is fulfilled by the passive avoidance of work. (see also the safeik of R’ Akiva Eiger on perek 5 of mishnayos shabbos re: the issur of shvisas b’heima).