The point to any preparation for any adverse event is to prepare more than one solution to a problem, and to have a solid understanding of your actual adversary. By asking that question, you have already defeated yourself on the sake of whomever you have decided is the dominant force. This is the sort of nihilism that stops us from meaningful change, because we destroy ourselves in either sloth or despair.

Won't they get jammed? Yes, absolutely, on local levels. This is electronic warfare and happens in any actual battlespace.

Does that mean it is completely useless in emergency situations (of which civil war is one)? No.

Meshtastic works on commercial frequencies. If they block those then a good number of non-wifi/bluetooth devices will just stop working.

Including, but not limited to: garage door openers, some (older) car key fobs, some RC equipment, wireless weather sensors, remotely readable metering devices (electricity, water) and a crapton of other things.

Jamming is a double-edged sword, there are common frequency bands used by everyones equipment like 2.4GHz, 5GHz or the ISM band. If you jam those indiscriminately, your own stuff stops working as well.

Any actual adversarial situation is a constant back and forth of "This works, whoops now it's countered, well now we countered that" forever.

Things don't stand still in "war". There's no "Solution" that will not be attacked, and there's no attack that cannot be worked around.

The US is huge — you can’t jam everything everywhere. Talking about just cities, you still can’t jam everything everywhere.

But yes, targeted suppression/oppression (depending on your allegiance) will almost certainly use jamming — in fact, I’ve spoken with some Antifa about how they jam EMS frequencies at their events.