In most cases. However, there are people who are intersex or similar which complicates things even though a separate issue to trans women participating in elite female sport.There aren't any complexities defining biological sex. It can be tested, it can be observed, it can be explained. You're looking for some rope to make an idiotic point when there is none.
Your second sentence is a totally different point, and has no bearing on the first.
Referring to trans women as biological men is insulting depending on the context. To demean / belittle in public etc - yes. To discuss whether they should be allowed in women sports on an online forum - not at all.
People who insist on referring to trans women as men are almost universally transphobic in my experience. Even if they don't think they are.