Hallo! Thank you for the answer.
I know that Molly backup is already encrypted. Basically, I would simply need an app that would syncthe folder chosen to back up Molly with Proton drive folder, in order to have a copy of the backup file in cloud. However, I thought that using Cryptomator, I could put other unencrypted files (e.g. a periodic backup of SMS) in the same folder as Molly backup and transfer them encrypted to the Proton Drive folder. I don't think it's a problem if an already encrypted file, like the Molly backup, is encrypted a second time.
In any case, I think there are three possible strategies:
1) See if I can select a subfolder of Proton Drive that can also be viewed offline as the destination folder of Molly's backup (programming it to sync only via wi-fi);
2) See if the Proton Drive app allows me to select a folder on my device's storage and schedule a sync with the cloud;
3) Install an app that can sync a folder on my device with my Proton Drive folder. I have already tried to follow the first two options, which are the most effective, but I have not succeeded. If you know of a way to make this possible, I might try again. For the third option I had thought of Cryptomator, but if you have other apps to suggest, I could try those.
Thank you