There's only one secret achievement. When you're looking at your Tank Mechanic Simulator it does hide it, but you can view the public achievement rates at the top of your personal achievement list, and it displays them all there.

Most achievements are achievable in normal game play. However there were 2 special achievements released in patches during Halloween and Christmas 2021. Unfortunately, if you missed those patches you will have to wait for Halloween/ Christmas of this year to get them. I only need the Halloween to get 100%. I'll have to wait unless someone makes a 'mod' before then.

Have you tried setting your computers calendar to that date?

Originally posted by Tailz:

Have you tried setting your computers calendar to that date?

Doesn't work, it's a patch before and after the event.

If you really don't want to wait and don't care about it other than just having it complete, there's a program called Steam Achievement Manager I believe, that'll let you simply mark them as such and it can actually update your Steam profile as though you had unlocked them the usual way.