Yes but if they catch you it cost like 60€ or so and legally counts as uh trespassing I think not that the BVG will bother to sue or anything.
So for locals it's still a grate deal.
And the tickets show how long they have been active, so activating them when you see they check might not pass at all (depending on the person checking, the often let it pass anyway).
But I have seen multiple cases of Ticket controlling sub-contractors acting out of line against Berlin citizens you could describe of "looking German" ("looking German" from the POV of a potential racist person, not mine POV).
I also have seen people acting out of line against the ticket controlling sub-contractors, including in the way the contractors claimed the black person did. But also worse. Like to a point where I was surprised the contractor kept calm and half expected needing to step in. Because many people would have lost it if "insulted" to that degree.
The increased tension between contractors and citizens in recent was the reason they changed their policy recently (for some time? still ongoing? idk.) to no longer have the subcontractors wear civil clothes even through it means they will miss more people without tickets. I also have seen more security people (which job does not include controlling tickets, luckily this is kept separate).
Germany is a relatively high-trust based society, so in Berlin you don't have turnstiles like other cities. However if you are caught riding without a ticket, the fine is 60€ for the first 2 offences and goes up after that.
Source: just came back from a week long trip to Berlin and I still have 2/4 tickets unused.