Hello Caroline Danda,
AxCrypt app full fill your requirement. AxCrypt is a user-mode and an independent app. You can encrypt the file(s) using the AxCrypt app. AxCrypt is a simple file encryption software with strong encryption. You can encrypt the local files and cloud files.
You can use AxCrypt to secure your files which are all stored in your cloud service like Google drive, one drive, Dropbox, etc..
AxCrypt Cloud Storage Awareness is really just about detecting installed cloud services, creating a “My AxCrypt” folder and then designating the created folder as ‘Secured’. However, the feature is really useful only when the folder is Secured, i.e. monitored for new files to encrypt.
After synchronizing your Google Drive files to your local, just encrypt those with the AxCrypt app. Once again sync your local with Google drive.
Please check out our video tutorials at https://www.youtube.com/channel/UCoSoXBjq6iCG5232fHoWStA and our other documentation at https://www.axcrypt.net/information/get-started/ to get started with AxCrypt.