Asking, "How do we know the Earth is round? Can we test it?" is very, very different than asserting, "The Earth is flat and I'll prove it experimentally."
Yes, 2 + 2 does not equal 5, but we need more people who can explain and think about _why_, and not simply repeat "just because". If someone cannot debunk a misconception as rudimentary as that, how can we expect their arguments against a flat earth theory to be sound and persuasive?
You see how people get pulled into the theory, get marginalized by society and how their family ends up becoming the flat earth community (even though they've never met).
You also see how hard it is for scientists with overwhelming evidence to convince them, it's a sobering watch.
In fact, you could probably create a number system, or a mathematics where 2+2=5 (simple example would be a number system the same as we have now, but the symbols for 4 and 5 are swapped). There are interesting ideas to be gained in thinking about what numbers mean, and imply based on questioning that.
However, once you’ve accepted all the definitions, and the number system, and the rules of the system you’ve accepted necessarily imply 2+2=4 then insisting that 2+2=5 is nonsensical. That’s the level at which the flat earth era are operating.
The proofs for round earth are not as trivial. People have varying degrees of skepticism. Some are genuinely curious and are convinced by demonstrations while others are just contrarians. If you've ever heard Eddie Bravo talk, it's clear he doesn't care about understanding what shape the earth is and just likes to spout conspiracies.
Science is always cool. Brain washing not so much.
It's unreasonable to start from a position of "all scientists are forced by boogeyman governments to say that the earth is flat", which is not a strawman and something you can in fact see them argue.