I may need to visit the United States briefly, therefore I want to offline backup my text messages and signal messages from my GrapheneOS phone. Once I return home I want to restore my data from the offline backup. Does anybody have experience and recommendations for this?
Like others have noted, for signal do a backup using the built-in feature. Then wipe the apps storage to clear messages.
For SMS/MMS I have usedSMS Import/Export before to transfer that data between devices easily without any issues so it should work as well.
I would also make sure to enable the feature to disable USB when the screen is locked. Just in case you get TSA stopped & they take your device for any reason.