I was a contributor to a mesh communication app called Briar. Briar has no central server, messages are synced only between users. All metadata and content are end-to-end encrypted. Briar doesn't rely on an internet connection, it can work over Wi-Fi and Bluetooth.
Since I am a member of the Guardians of Hong Kong group, I know that it's been used among Hong Kong protesters and it proved useful. Check it out for more info, if you will: https://briarproject.org
Take heart! God bless🙏🏻
just to let you know, i am not myself in myanmar. i'm hoping to give some helpful software or information to anyone who needs it over there. this is definitely something to consider, and it seems the intranet of devices is the real solution here, as QR codes probably would be too large to store the necessary amount of pure text, and i'm not sure a QR reader offline would even be able to interpret it, which requires developing something new. Another commenter posted about BriarProject.org which is your idea but implemented into a mesh messaging protocol.