That's the propagandist's argument. But the reality is there is a difference between truth and falsehood, it's not just a matter of perception, and we can tell the difference with reasonable accuracy.

>there is a difference between truth and falsehood

Of course, but that's distinct from propaganda vs non-propaganda. A foreign actor can secretly pay for a marketing campaign that spreads the truth. A scientist can make an honest mistake and spread a falsehood.

>we can tell the difference with reasonable accuracy.

Depends on the claim. Suppose I tell you that exactly one year from now, at your current location, it will be raining. Is that true or false?

It's a game of perfect philosophical definitions, which generally are not needed in practical life.

Well sure, how about a "good enough in practice" definition instead? Because in practice, there's a big definition dispute here.