On Android, it is possible to save images directly from a website to Cryptomator using the “share image” feature of Chrome.
However, when using this feature, Chrome assigns a probably randomly generated long numeric file name. This is undesirable; Say, I want to save artworks or webcomic pages; In both cases, the file name often contains useful metadata (date or page number of comic pages, artist name, artwork title).
Using Chrome’s “download” button preserves the file name, but does not allow to choose a download location, even when “ask where to save files” is enabled in the settings and even if it did, until the document provider feature is implemented, it wouldn’t help much anyway.
The same applies to Firefox (no “ask for location option”, randomly generated file name when sharing).
I’m not 100% certain but I think that in order to do what you want you will need the document provider feature whenever it becomes a reality.
I’ve tried several ways to figure it out and I don’t find a solution.
On desktop operating systems there is a virtual file system typically using fuse and that way it would work but there is no option for that on Android.
The main obstacle is the software Keys itself on encrypting the files before they get uploaded to the cloud so the cryptomator software has to take the file from somewhere and encrypt it and put it up on the internet and in order to do that it needs to be able to talk directly to your browser and it can’t.
If you could mount evolved when you unlock it like you do on desktop operating system and it would be a solution for some folks.
I have a Samsung phone and the Samsung web browser is a chromium based browser and in settings it has the ability to change the default download location and if there was a valid Mount point for the vault then you could select that as the location but again it cannot be done.