Is there a heter for inviting a non-jew in the process of conversion for Yom Tov?
How will they know what a yontiff meal really is, or how to do one, and therefore be able to commit to making their own upon conversion, without having been to any?
The problem is that cooking on Yom Tov is only permissible if the food is intended for a Jew. There are ways to invite the non-Jew as an afterthought or "accidentally" make extra.
Some of this is a Fence. My former rabbi (who is more particular than most) held that one could not even revert to Shabbos-mode entertaining lest he forget and do a Yom Tov cooking activity for the non-Jew.
One is allowed, however, to serve only cold food and invite the Non-Jew.
Of course, my ex-rabbi could have been exceedingly stringent on himself (and his congregants) so not only CYLOR, but consult several rabbis to find where the actual issur ends and the fences begin.