I appreciate that you have posted this nearly 3 years ago but i had the same issue. The way i got my data over to QGIS is as follows:

1. In QField go to 'open local file' open 'QField files directory' then 'imported project'

2. Instead of clicking to go into the folder click on the three dots at the side, there should be the option to 'export to folder' choose where you want the exported data to be saved.

3. with your tablet plugged in copy and paste the exported data onto your computer.

4. in QGIS go to 'plugins' then 'Qfield sync' then 'syncroise from QField' locate your folder and finaly select 'syncronise'

hopefully this makes sense

I appreciate that you have posted this nearly 3 years ago but I had the same issue. The way I got my data over to QGIS is as follows:

1. In QField go to 'open local file' open 'QField files directory' then 'imported project'
2. Instead of clicking to go into the folder click on the three dots at the side, there should be the option to 'export to folder' choose where you want the exported data to be saved.
3. With your tablet plugged in copy and paste the exported data onto your computer.
4. In QGIS go to 'plugins' then 'Qfield sync' then 'synchronize from QField' locate your folder and finally select 'synchronize'