Hi.
I moved your question to a new topic as it is not related to the topic you choose.
Cryptomator desktop is designed to work with as many cloud storages as possible. This is achieved by using the storage providers solution of accessing your vault, which is in most of the cases a sync client.
So the design is not focused on local disc space consumption, but on provider compatibility.
With the mobile apps it’s different as here local disc storage is often an issue. So it was decided to design them in a way to not consume much local space, but at the cost of compatibility with some storage providers.
Or in short: I don’t think that direct access to online vaults will be a desktop feature in the near future.
But maybe you are interested in this solution: