For the record, here is what I did to backup the FreeOTP information from one Android (Lineageos) mobile and restore them to another one. The FreeOTP app was installed on the new phone.
- with developers options active (tap 7 times on the kernel build number in settings > about phone) go to settings > developers options and set Android debugging
- plugin the mobile to the USB port
- adb backup -f ~/android-org.fedorahosted.freeotp.adb org.fedorahosted.freeotp
- type a password on the old phone
- adb restore ~/android-org.fedorahosted.freeotp.adb
- type the same password
- open FreeOTP to verify the data is available