massive privacy violation - you can see everyone's courses and home start

I think all courses are public, and this is intentional, but notice that courses (including this particular one) are in no way associated with a garmin connect account, or at least this information is not publicly available, so although you see a colorful line on a map this does not necessarily reveal any personal information about anybody.

No, that´s not true. You are able to "lock" your activities. For you only, your friends or all of your connections.
Also it is possible to lock all new activities by default.

Try:
https://connect.garmin.com/modern/activity/1309755310

I agree that this is not correct. I just tried to access one of my courses that's marked private while logged out and it gave me an error rather than show the course. Both activities and courses support this feature.

Ah, yes! Now I see it. A course can indeed be locked. However if you select OpenStreetMap for your course a warning appears that this course will be made public, although anonymous. Hence my confusion.

This is shown, when I access one of my (private) activities without being logged in:

348

This is shown, when I access one of my (private) activities without being logged in:

Well, yes, but we were talking about privacy of courses - not activities. That's a slightly different case.

Well, yes, but we were talking about privacy of courses - not activities. That's a slightly different case.

Well, this activity included a cource, so I thought, it should be similar.

It does not make any difference!

You have exactly the same Lock-Symbol on activities and courses.
The only difference is, you can only lock and unlock a course. Activities can be locked selective to friends, connections and youself (full lock).

Courses:
" />">

Activities:
" />">