This website contains age-restricted materials including nudity and explicit depictions of sexual activity.
By entering, you affirm that you are at least 18 years of age or the age of majority in the jurisdiction you are accessing the website from and you consent to viewing sexually explicit content.
Boosting a Lemmy post in Mastodon shows up as an upvote in Lemmy. So the two concepts seem to be coupled in the activitypub substructure. I don’t see how upvotes would be secret then, as I don’t think it’s possible to boost something privately on Mastodon.
You are exactly right - the underlying protocol (ActivityPub) has no concept of private votes. Making them private would only hide them in Lemmy’s UI, but still make them accessible to other users using other apps.
Looks like PieFed is experimenting with a potential workaround.