[2020] Did you ever see IRL a tank you saw/have in game?

Plenty of them.

I often run behind Soviet/Polish bad boys in park

As addition, I was in Kubinka, so I was able to see all the RUSSIAN BIAS live.

And Maus. It's hidden behind Mortar "Adam". Yes, there is a mobile mortar that is so huge, you can hide Maus behind it

You mean something like this:

https://warthunder.com/en/news/2886--en

(I saw that T-44 live, but from ~20-30m only)

If I remember correct it's Lim-1 / MiG-15 (Lim-1 is licensed version of MiG-15 produced in Poland)