If you've got the steam mobile app for Android for 2fa and want to move to a different app that supports steam 2fa (aegis, winauth, etc), use steam auth on multiple devices, or simply move to a new device without a temporary trade block, version 2.1.4 of the steam app will allow you to perform adb backups; Android backup extractor will allow you to convert the backup to a standard tar file to extract the secrets if you want to.