Thanks to some funding from Xi'an Jiaotong-Liverpool University we have now added support for the mobile app to the attendance activity.
The latest code has not yet been released in the moodle.org plugins db (coming soon) but is available in the master branch in the github repository and is compatible with Moodle 3.5 if you want to try it out.
Both student self-marking and basic teacher marking of attendances is currently supported for the current sessions. (If teachers want to update older sessions they will need to do this within the normal site.)
If you find any issues with the mobile app support, please create a new tracker issue at: